drm/amd/display: Try RGB before YCbCr 4:4:4 in stream validationgrafted

amdgpu_dm_create_validate_stream_for_sink() walks encoding_order[] and
uses the first encoding that validates. YCbCr 4:4:4 is listed before
RGB, so an HDMI sink that advertises 4:4:4 gets YCbCr 4:4:4 whenever the
"color format" property is left at AUTO, even though RGB fits the same
link.

That contradicts the documented AUTO behaviour for HDMI in enum
drm_connector_color_format (RGB, falling back to YCbCr 4:2:0 only when
the bandwidth is not available or the mode is 4:2:0-only), which the
amdgpu implementation of the property also describes. It also leaves
the "Broadcast RGB" property without effect on such sinks, since the
quantization range it selects only applies to RGB output.

Try RGB first. The mask still holds every encoding the sink supports,
so a mode that cannot carry RGB falls back exactly as before.

For reference, v7.2 picked RGB here unless YCbCr 4:4:4 was forced
through debugfs, while earlier kernels picked YCbCr 4:4:4 for any HDMI
sink that advertised it.

Fixes: 0b0ff65d3ca1 ("drm/amd/display: Refactor stream validation")
Suggested-by: Adolfo Rodrigues <adolfotregosa@gmail.com>
Assisted-by: Claude Code:claude-fable-5-1
Signed-off-by: Adrian Betschart <adrian.betschart@cinemaone.ch>
Reviewed-by: Fangzhi Zuo <jerry.zuo@amd.com>
Tested-by: Adolfo Rodrigues <adolfotregosa@gmail.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 7de432bc753133764dc40d37f9388da56de251e7)

5 files changed, 1206 insertions, 0 deletions

diff --git a/drivers/siox/Kconfig b/drivers/siox/Kconfig
new file mode 100644
index 000000000..4326db32c
--- /dev/null
+++ b/drivers/siox/Kconfig
@@ -0,0 +1,19 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menuconfig SIOX
+	tristate "Eckelmann SIOX Support"
+	help
+	  SIOX stands for Serial Input Output eXtension and is a synchronous
+	  bus system invented by Eckelmann AG. It is used in their control and
+	  remote monitoring systems for commercial and industrial refrigeration
+	  to drive additional I/O units.
+
+	  Unless you know better, it is probably safe to say "no" here.
+
+if SIOX
+
+config SIOX_BUS_GPIO
+	tristate "SIOX GPIO bus driver"
+	help
+	  SIOX bus driver that controls the four bus lines using GPIOs.
+
+endif
diff --git a/drivers/siox/Makefile b/drivers/siox/Makefile
new file mode 100644
index 000000000..8b5ebb1a8
--- /dev/null
+++ b/drivers/siox/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_SIOX) += siox-core.o
+obj-$(CONFIG_SIOX_BUS_GPIO) += siox-bus-gpio.o
diff --git a/drivers/siox/siox-bus-gpio.c b/drivers/siox/siox-bus-gpio.c
new file mode 100644
index 000000000..a0b62397e
--- /dev/null
+++ b/drivers/siox/siox-bus-gpio.c
@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015-2017 Pengutronix, Uwe Kleine-König <kernel@pengutronix.de>
+ */
+
+#include <linux/gpio/consumer.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+#include <linux/delay.h>
+
+#include "siox.h"
+
+#define DRIVER_NAME "siox-gpio"
+
+struct siox_gpio_ddata {
+	struct gpio_desc *din;
+	struct gpio_desc *dout;
+	struct gpio_desc *dclk;
+	struct gpio_desc *dld;
+};
+
+static unsigned int siox_clkhigh_ns = 1000;
+static unsigned int siox_loadhigh_ns;
+static unsigned int siox_bytegap_ns;
+
+static int siox_gpio_pushpull(struct siox_master *smaster,
+			      size_t setbuf_len, const u8 setbuf[],
+			      size_t getbuf_len, u8 getbuf[])
+{
+	struct siox_gpio_ddata *ddata = siox_master_get_devdata(smaster);
+	size_t i;
+	size_t cycles = max(setbuf_len, getbuf_len);
+
+	/* reset data and clock */
+	gpiod_set_value_cansleep(ddata->dout, 0);
+	gpiod_set_value_cansleep(ddata->dclk, 0);
+
+	gpiod_set_value_cansleep(ddata->dld, 1);
+	ndelay(siox_loadhigh_ns);
+	gpiod_set_value_cansleep(ddata->dld, 0);
+
+	for (i = 0; i < cycles; ++i) {
+		u8 set = 0, get = 0;
+		size_t j;
+
+		if (i >= cycles - setbuf_len)
+			set = setbuf[i - (cycles - setbuf_len)];
+
+		for (j = 0; j < 8; ++j) {
+			get <<= 1;
+			if (gpiod_get_value_cansleep(ddata->din))
+				get |= 1;
+
+			/* DOUT is logically inverted */
+			gpiod_set_value_cansleep(ddata->dout, !(set & 0x80));
+			set <<= 1;
+
+			gpiod_set_value_cansleep(ddata->dclk, 1);
+			ndelay(siox_clkhigh_ns);
+			gpiod_set_value_cansleep(ddata->dclk, 0);
+		}
+
+		if (i < getbuf_len)
+			getbuf[i] = get;
+
+		ndelay(siox_bytegap_ns);
+	}
+
+	gpiod_set_value_cansleep(ddata->dld, 1);
+	ndelay(siox_loadhigh_ns);
+	gpiod_set_value_cansleep(ddata->dld, 0);
+
+	/*
+	 * Resetting dout isn't necessary protocol wise, but it makes the
+	 * signals more pretty because the dout level is deterministic between
+	 * cycles. Note that this only affects dout between the master and the
+	 * first siox device. dout for the later devices depend on the output of
+	 * the previous siox device.
+	 */
+	gpiod_set_value_cansleep(ddata->dout, 0);
+
+	return 0;
+}
+
+static int siox_gpio_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct siox_gpio_ddata *ddata;
+	int ret;
+	struct siox_master *smaster;
+
+	smaster = devm_siox_master_alloc(dev, sizeof(*ddata));
+	if (!smaster)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, smaster);
+	ddata = siox_master_get_devdata(smaster);
+
+	ddata->din = devm_gpiod_get(dev, "din", GPIOD_IN);
+	if (IS_ERR(ddata->din))
+		return dev_err_probe(dev, PTR_ERR(ddata->din),
+				     "Failed to get din GPIO\n");
+
+	ddata->dout = devm_gpiod_get(dev, "dout", GPIOD_OUT_LOW);
+	if (IS_ERR(ddata->dout))
+		return dev_err_probe(dev, PTR_ERR(ddata->dout),
+				     "Failed to get dout GPIO\n");
+
+	ddata->dclk = devm_gpiod_get(dev, "dclk", GPIOD_OUT_LOW);
+	if (IS_ERR(ddata->dclk))
+		return dev_err_probe(dev, PTR_ERR(ddata->dclk),
+				     "Failed to get dclk GPIO\n");
+
+	ddata->dld = devm_gpiod_get(dev, "dld", GPIOD_OUT_LOW);
+	if (IS_ERR(ddata->dld))
+		return dev_err_probe(dev, PTR_ERR(ddata->dld),
+				     "Failed to get dld GPIO\n");
+
+	smaster->pushpull = siox_gpio_pushpull;
+	/* XXX: determine automatically like spi does */
+	smaster->busno = 0;
+
+	ret = devm_siox_master_register(dev, smaster);
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "Failed to register siox master\n");
+
+	return 0;
+}
+
+static const struct of_device_id siox_gpio_dt_ids[] = {
+	{ .compatible = "eckelmann,siox-gpio", },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, siox_gpio_dt_ids);
+
+static struct platform_driver siox_gpio_driver = {
+	.probe = siox_gpio_probe,
+
+	.driver = {
+		.name = DRIVER_NAME,
+		.of_match_table = siox_gpio_dt_ids,
+	},
+};
+module_platform_driver(siox_gpio_driver);
+
+MODULE_AUTHOR("Uwe Kleine-Koenig <u.kleine-koenig@pengutronix.de>");
+MODULE_DESCRIPTION("SIOX GPIO bus driver");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:" DRIVER_NAME);
diff --git a/drivers/siox/siox-core.c b/drivers/siox/siox-core.c
new file mode 100644
index 000000000..3e8f3b6a4
--- /dev/null
+++ b/drivers/siox/siox-core.c
@@ -0,0 +1,980 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015-2017 Pengutronix, Uwe Kleine-König <kernel@pengutronix.de>
+ */
+#include <linux/kernel.h>
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/sysfs.h>
+
+#include "siox.h"
+
+/*
+ * The lowest bit in the SIOX status word signals if the in-device watchdog is
+ * ok. If the bit is set, the device is functional.
+ *
+ * On writing the watchdog timer is reset when this bit toggles.
+ */
+#define SIOX_STATUS_WDG			0x01
+
+/*
+ * Bits 1 to 3 of the status word read as the bitwise negation of what was
+ * clocked in before. The value clocked in is changed in each cycle and so
+ * allows to detect transmit/receive problems.
+ */
+#define SIOX_STATUS_COUNTER		0x0e
+
+/*
+ * Each Siox-Device has a 4 bit type number that is neither 0 nor 15. This is
+ * available in the upper nibble of the read status.
+ *
+ * On write these bits are DC.
+ */
+#define SIOX_STATUS_TYPE		0xf0
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/siox.h>
+
+static bool siox_is_registered;
+
+static void siox_master_lock(struct siox_master *smaster)
+{
+	mutex_lock(&smaster->lock);
+}
+
+static void siox_master_unlock(struct siox_master *smaster)
+{
+	mutex_unlock(&smaster->lock);
+}
+
+static inline u8 siox_status_clean(u8 status_read, u8 status_written)
+{
+	/*
+	 * bits 3:1 of status sample the respective bit in the status
+	 * byte written in the previous cycle but inverted. So if you wrote the
+	 * status word as 0xa before (counter = 0b101), it is expected to get
+	 * back the counter bits as 0b010.
+	 *
+	 * So given the last status written this function toggles the there
+	 * unset counter bits in the read value such that the counter bits in
+	 * the return value are all zero iff the bits were read as expected to
+	 * simplify error detection.
+	 */
+
+	return status_read ^ (~status_written & 0xe);
+}
+
+static bool siox_device_counter_error(struct siox_device *sdevice,
+				      u8 status_clean)
+{
+	return (status_clean & SIOX_STATUS_COUNTER) != 0;
+}
+
+static bool siox_device_type_error(struct siox_device *sdevice, u8 status_clean)
+{
+	u8 statustype = (status_clean & SIOX_STATUS_TYPE) >> 4;
+
+	/*
+	 * If the device knows which value the type bits should have, check
+	 * against this value otherwise just rule out the invalid values 0b0000
+	 * and 0b1111.
+	 */
+	if (sdevice->statustype) {
+		if (statustype != sdevice->statustype)
+			return true;
+	} else {
+		switch (statustype) {
+		case 0:
+		case 0xf:
+			return true;
+		}
+	}
+
+	return false;
+}
+
+static bool siox_device_wdg_error(struct siox_device *sdevice, u8 status_clean)
+{
+	return (status_clean & SIOX_STATUS_WDG) == 0;
+}
+
+/*
+ * If there is a type or counter error the device is called "unsynced".
+ */
+bool siox_device_synced(struct siox_device *sdevice)
+{
+	if (siox_device_type_error(sdevice, sdevice->status_read_clean))
+		return false;
+
+	return !siox_device_counter_error(sdevice, sdevice->status_read_clean);
+
+}
+EXPORT_SYMBOL_GPL(siox_device_synced);
+
+/*
+ * A device is called "connected" if it is synced and the watchdog is not
+ * asserted.
+ */
+bool siox_device_connected(struct siox_device *sdevice)
+{
+	if (!siox_device_synced(sdevice))
+		return false;
+
+	return !siox_device_wdg_error(sdevice, sdevice->status_read_clean);
+}
+EXPORT_SYMBOL_GPL(siox_device_connected);
+
+static void siox_poll(struct siox_master *smaster)
+{
+	struct siox_device *sdevice;
+	size_t i = smaster->setbuf_len;
+	unsigned int devno = 0;
+	int unsync_error = 0;
+
+	smaster->last_poll = jiffies;
+
+	/*
+	 * The counter bits change in each second cycle, the watchdog bit
+	 * toggles each time.
+	 * The counter bits hold values from [0, 6]. 7 would be possible
+	 * theoretically but the protocol designer considered that a bad idea
+	 * for reasons unknown today. (Maybe that's because then the status read
+	 * back has only zeros in the counter bits then which might be confused
+	 * with a stuck-at-0 error. But for the same reason (with s/0/1/) 0
+	 * could be skipped.)
+	 */
+	if (++smaster->status > 0x0d)
+		smaster->status = 0;
+
+	memset(smaster->buf, 0, smaster->setbuf_len);
+
+	/* prepare data pushed out to devices in buf[0..setbuf_len) */
+	list_for_each_entry(sdevice, &smaster->devices, node) {
+		struct siox_driver *sdriver =
+			to_siox_driver(sdevice->dev.driver);
+		sdevice->status_written = smaster->status;
+
+		i -= sdevice->inbytes;
+
+		/*
+		 * If the device or a previous one is unsynced, don't pet the
+		 * watchdog. This is done to ensure that the device is kept in
+		 * reset when something is wrong.
+		 */
+		if (!siox_device_synced(sdevice))
+			unsync_error = 1;
+
+		if (sdriver && !unsync_error)
+			sdriver->set_data(sdevice, sdevice->status_written,
+					  &smaster->buf[i + 1]);
+		else
+			/*
+			 * Don't trigger watchdog if there is no driver or a
+			 * sync problem
+			 */
+			sdevice->status_written &= ~SIOX_STATUS_WDG;
+
+		smaster->buf[i] = sdevice->status_written;
+
+		trace_siox_set_data(smaster, sdevice, devno, i);
+
+		devno++;
+	}
+
+	smaster->pushpull(smaster, smaster->setbuf_len, smaster->buf,
+			  smaster->getbuf_len,
+			  smaster->buf + smaster->setbuf_len);
+
+	unsync_error = 0;
+
+	/* interpret data pulled in from devices in buf[setbuf_len..] */
+	devno = 0;
+	i = smaster->setbuf_len;
+	list_for_each_entry(sdevice, &smaster->devices, node) {
+		struct siox_driver *sdriver =
+			to_siox_driver(sdevice->dev.driver);
+		u8 status = smaster->buf[i + sdevice->outbytes - 1];
+		u8 status_clean;
+		u8 prev_status_clean = sdevice->status_read_clean;
+		bool synced = true;
+		bool connected = true;
+
+		if (!siox_device_synced(sdevice))
+			unsync_error = 1;
+
+		/*
+		 * If the watchdog bit wasn't toggled in this cycle, report the
+		 * watchdog as active to give a consistent view for drivers and
+		 * sysfs consumers.
+		 */
+		if (!sdriver || unsync_error)
+			status &= ~SIOX_STATUS_WDG;
+
+		status_clean =
+			siox_status_clean(status,
+					  sdevice->status_written_lastcycle);
+
+		/* Check counter and type bits */
+		if (siox_device_counter_error(sdevice, status_clean) ||
+		    siox_device_type_error(sdevice, status_clean)) {
+			bool prev_error;
+
+			synced = false;
+
+			/* only report a new error if the last cycle was ok */
+			prev_error =
+				siox_device_counter_error(sdevice,
+							  prev_status_clean) ||
+				siox_device_type_error(sdevice,
+						       prev_status_clean);
+
+			if (!prev_error) {
+				sdevice->status_errors++;
+				sysfs_notify_dirent(sdevice->status_errors_kn);
+			}
+		}
+
+		/* If the device is unsynced report the watchdog as active */
+		if (!synced) {
+			status &= ~SIOX_STATUS_WDG;
+			status_clean &= ~SIOX_STATUS_WDG;
+		}
+
+		if (siox_device_wdg_error(sdevice, status_clean))
+			connected = false;
+
+		/* The watchdog state changed just now */
+		if ((status_clean ^ prev_status_clean) & SIOX_STATUS_WDG) {
+			sysfs_notify_dirent(sdevice->watchdog_kn);
+
+			if (siox_device_wdg_error(sdevice, status_clean)) {
+				struct kernfs_node *wd_errs =
+					sdevice->watchdog_errors_kn;
+
+				sdevice->watchdog_errors++;
+				sysfs_notify_dirent(wd_errs);
+			}
+		}
+
+		if (connected != sdevice->connected)
+			sysfs_notify_dirent(sdevice->connected_kn);
+
+		sdevice->status_read_clean = status_clean;
+		sdevice->status_written_lastcycle = sdevice->status_written;
+		sdevice->connected = connected;
+
+		trace_siox_get_data(smaster, sdevice, devno, status_clean, i);
+
+		/* only give data read to driver if the device is connected */
+		if (sdriver && connected)
+			sdriver->get_data(sdevice, &smaster->buf[i]);
+
+		devno++;
+		i += sdevice->outbytes;
+	}
+}
+
+static int siox_poll_thread(void *data)
+{
+	struct siox_master *smaster = data;
+	signed long timeout = 0;
+
+	get_device(&smaster->dev);
+
+	for (;;) {
+		if (kthread_should_stop()) {
+			put_device(&smaster->dev);
+			return 0;
+		}
+
+		siox_master_lock(smaster);
+
+		if (smaster->active) {
+			unsigned long next_poll =
+				smaster->last_poll + smaster->poll_interval;
+			if (time_is_before_eq_jiffies(next_poll))
+				siox_poll(smaster);
+
+			timeout = smaster->poll_interval -
+				(jiffies - smaster->last_poll);
+		} else {
+			timeout = MAX_SCHEDULE_TIMEOUT;
+		}
+
+		/*
+		 * Set the task to idle while holding the lock. This makes sure
+		 * that we don't sleep too long when the bus is reenabled before
+		 * schedule_timeout is reached.
+		 */
+		if (timeout > 0)
+			set_current_state(TASK_IDLE);
+
+		siox_master_unlock(smaster);
+
+		if (timeout > 0)
+			schedule_timeout(timeout);
+
+		/*
+		 * I'm not clear if/why it is important to set the state to
+		 * RUNNING again, but it fixes a "do not call blocking ops when
+		 * !TASK_RUNNING;"-warning.
+		 */
+		set_current_state(TASK_RUNNING);
+	}
+}
+
+static int __siox_start(struct siox_master *smaster)
+{
+	if (!(smaster->setbuf_len + smaster->getbuf_len))
+		return -ENODEV;
+
+	if (!smaster->buf)
+		return -ENOMEM;
+
+	if (smaster->active)
+		return 0;
+
+	smaster->active = 1;
+	wake_up_process(smaster->poll_thread);
+
+	return 1;
+}
+
+static int siox_start(struct siox_master *smaster)
+{
+	int ret;
+
+	siox_master_lock(smaster);
+	ret = __siox_start(smaster);
+	siox_master_unlock(smaster);
+
+	return ret;
+}
+
+static int __siox_stop(struct siox_master *smaster)
+{
+	if (smaster->active) {
+		struct siox_device *sdevice;
+
+		smaster->active = 0;
+
+		list_for_each_entry(sdevice, &smaster->devices, node) {
+			if (sdevice->connected)
+				sysfs_notify_dirent(sdevice->connected_kn);
+			sdevice->connected = false;
+		}
+
+		return 1;
+	}
+	return 0;
+}
+
+static int siox_stop(struct siox_master *smaster)
+{
+	int ret;
+
+	siox_master_lock(smaster);
+	ret = __siox_stop(smaster);
+	siox_master_unlock(smaster);
+
+	return ret;
+}
+
+static ssize_t type_show(struct device *dev,
+			 struct device_attribute *attr, char *buf)
+{
+	struct siox_device *sdev = to_siox_device(dev);
+
+	return sprintf(buf, "%s\n", sdev->type);
+}
+
+static DEVICE_ATTR_RO(type);
+
+static ssize_t inbytes_show(struct device *dev,
+			    struct device_attribute *attr, char *buf)
+{
+	struct siox_device *sdev = to_siox_device(dev);
+
+	return sprintf(buf, "%zu\n", sdev->inbytes);
+}
+
+static DEVICE_ATTR_RO(inbytes);
+
+static ssize_t outbytes_show(struct device *dev,
+			     struct device_attribute *attr, char *buf)
+{
+	struct siox_device *sdev = to_siox_device(dev);
+
+	return sprintf(buf, "%zu\n", sdev->outbytes);
+}
+
+static DEVICE_ATTR_RO(outbytes);
+
+static ssize_t status_errors_show(struct device *dev,
+				  struct device_attribute *attr, char *buf)
+{
+	struct siox_device *sdev = to_siox_device(dev);
+	unsigned int status_errors;
+
+	siox_master_lock(sdev->smaster);
+
+	status_errors = sdev->status_errors;
+
+	siox_master_unlock(sdev->smaster);
+
+	return sprintf(buf, "%u\n", status_errors);
+}
+
+static DEVICE_ATTR_RO(status_errors);
+
+static ssize_t connected_show(struct device *dev,
+			      struct device_attribute *attr, char *buf)
+{
+	struct siox_device *sdev = to_siox_device(dev);
+	bool connected;
+
+	siox_master_lock(sdev->smaster);
+
+	connected = sdev->connected;
+
+	siox_master_unlock(sdev->smaster);
+
+	return sprintf(buf, "%u\n", connected);
+}
+
+static DEVICE_ATTR_RO(connected);
+
+static ssize_t watchdog_show(struct device *dev,
+			     struct device_attribute *attr, char *buf)
+{
+	struct siox_device *sdev = to_siox_device(dev);
+	u8 status;
+
+	siox_master_lock(sdev->smaster);
+
+	status = sdev->status_read_clean;
+
+	siox_master_unlock(sdev->smaster);
+
+	return sprintf(buf, "%d\n", status & SIOX_STATUS_WDG);
+}
+
+static DEVICE_ATTR_RO(watchdog);
+
+static ssize_t watchdog_errors_show(struct device *dev,
+				    struct device_attribute *attr, char *buf)
+{
+	struct siox_device *sdev = to_siox_device(dev);
+	unsigned int watchdog_errors;
+
+	siox_master_lock(sdev->smaster);
+
+	watchdog_errors = sdev->watchdog_errors;
+
+	siox_master_unlock(sdev->smaster);
+
+	return sprintf(buf, "%u\n", watchdog_errors);
+}
+
+static DEVICE_ATTR_RO(watchdog_errors);
+
+static struct attribute *siox_device_attrs[] = {
+	&dev_attr_type.attr,
+	&dev_attr_inbytes.attr,
+	&dev_attr_outbytes.attr,
+	&dev_attr_status_errors.attr,
+	&dev_attr_connected.attr,
+	&dev_attr_watchdog.attr,
+	&dev_attr_watchdog_errors.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(siox_device);
+
+static void siox_device_release(struct device *dev)
+{
+	struct siox_device *sdevice = to_siox_device(dev);
+
+	kfree(sdevice);
+}
+
+static const struct device_type siox_device_type = {
+	.groups = siox_device_groups,
+	.release = siox_device_release,
+};
+
+static int siox_match(struct device *dev, const struct device_driver *drv)
+{
+	if (dev->type != &siox_device_type)
+		return 0;
+
+	/* up to now there is only a single driver so keeping this simple */
+	return 1;
+}
+
+static int siox_probe(struct device *dev)
+{
+	struct siox_driver *sdriver = to_siox_driver(dev->driver);
+	struct siox_device *sdevice = to_siox_device(dev);
+
+	return sdriver->probe(sdevice);
+}
+
+static void siox_remove(struct device *dev)
+{
+	struct siox_driver *sdriver =
+		container_of(dev->driver, struct siox_driver, driver);
+	struct siox_device *sdevice = to_siox_device(dev);
+
+	if (sdriver->remove)
+		sdriver->remove(sdevice);
+}
+
+static void siox_shutdown(struct device *dev)
+{
+	struct siox_device *sdevice = to_siox_device(dev);
+	struct siox_driver *sdriver;
+
+	if (!dev->driver)
+		return;
+
+	sdriver = container_of(dev->driver, struct siox_driver, driver);
+	if (sdriver->shutdown)
+		sdriver->shutdown(sdevice);
+}
+
+static const struct bus_type siox_bus_type = {
+	.name = "siox",
+	.match = siox_match,
+	.probe = siox_probe,
+	.remove = siox_remove,
+	.shutdown = siox_shutdown,
+};
+
+static ssize_t active_show(struct device *dev,
+			   struct device_attribute *attr, char *buf)
+{
+	struct siox_master *smaster = to_siox_master(dev);
+
+	return sprintf(buf, "%d\n", smaster->active);
+}
+
+static ssize_t active_store(struct device *dev,
+			    struct device_attribute *attr,
+			    const char *buf, size_t count)
+{
+	struct siox_master *smaster = to_siox_master(dev);
+	int ret;
+	int active;
+
+	ret = kstrtoint(buf, 0, &active);
+	if (ret < 0)
+		return ret;
+
+	if (active)
+		ret = siox_start(smaster);
+	else
+		ret = siox_stop(smaster);
+
+	if (ret < 0)
+		return ret;
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(active);
+
+static struct siox_device *siox_device_add(struct siox_master *smaster,
+					   const char *type, size_t inbytes,
+					   size_t outbytes, u8 statustype);
+
+static ssize_t device_add_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	struct siox_master *smaster = to_siox_master(dev);
+	int ret;
+	char type[20] = "";
+	size_t inbytes = 0, outbytes = 0;
+	u8 statustype = 0;
+
+	ret = sscanf(buf, "%19s %zu %zu %hhu", type, &inbytes,
+		     &outbytes, &statustype);
+	if (ret != 3 && ret != 4)
+		return -EINVAL;
+
+	if (strcmp(type, "siox-12x8") || inbytes != 2 || outbytes != 4)
+		return -EINVAL;
+
+	siox_device_add(smaster, "siox-12x8", inbytes, outbytes, statustype);
+
+	return count;
+}
+
+static DEVICE_ATTR_WO(device_add);
+
+static void siox_device_remove(struct siox_master *smaster);
+
+static ssize_t device_remove_store(struct device *dev,
+				   struct device_attribute *attr,
+				   const char *buf, size_t count)
+{
+	struct siox_master *smaster = to_siox_master(dev);
+
+	/* XXX? require to write <type> <inbytes> <outbytes> */
+	siox_device_remove(smaster);
+
+	return count;
+}
+
+static DEVICE_ATTR_WO(device_remove);
+
+static ssize_t poll_interval_ns_show(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	struct siox_master *smaster = to_siox_master(dev);
+
+	return sprintf(buf, "%lld\n", jiffies_to_nsecs(smaster->poll_interval));
+}
+
+static ssize_t poll_interval_ns_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t count)
+{
+	struct siox_master *smaster = to_siox_master(dev);
+	int ret;
+	u64 val;
+
+	ret = kstrtou64(buf, 0, &val);
+	if (ret < 0)
+		return ret;
+
+	siox_master_lock(smaster);
+
+	smaster->poll_interval = nsecs_to_jiffies(val);
+
+	siox_master_unlock(smaster);
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(poll_interval_ns);
+
+static struct attribute *siox_master_attrs[] = {
+	&dev_attr_active.attr,
+	&dev_attr_device_add.attr,
+	&dev_attr_device_remove.attr,
+	&dev_attr_poll_interval_ns.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(siox_master);
+
+static void siox_master_release(struct device *dev)
+{
+	struct siox_master *smaster = to_siox_master(dev);
+
+	kfree(smaster);
+}
+
+static const struct device_type siox_master_type = {
+	.groups = siox_master_groups,
+	.release = siox_master_release,
+};
+
+struct siox_master *siox_master_alloc(struct device *dev,
+				      size_t size)
+{
+	struct siox_master *smaster;
+
+	if (!dev)
+		return NULL;
+
+	smaster = kzalloc(sizeof(*smaster) + size, GFP_KERNEL);
+	if (!smaster)
+		return NULL;
+
+	device_initialize(&smaster->dev);
+
+	smaster->busno = -1;
+	smaster->dev.bus = &siox_bus_type;
+	smaster->dev.type = &siox_master_type;
+	smaster->dev.parent = dev;
+	smaster->poll_interval = DIV_ROUND_UP(HZ, 40);
+
+	dev_set_drvdata(&smaster->dev, &smaster[1]);
+
+	return smaster;
+}
+EXPORT_SYMBOL_GPL(siox_master_alloc);
+
+static void devm_siox_master_put(void *data)
+{
+	struct siox_master *smaster = data;
+
+	siox_master_put(smaster);
+}
+
+struct siox_master *devm_siox_master_alloc(struct device *dev,
+					   size_t size)
+{
+	struct siox_master *smaster;
+	int ret;
+
+	smaster = siox_master_alloc(dev, size);
+	if (!smaster)
+		return NULL;
+
+	ret = devm_add_action_or_reset(dev, devm_siox_master_put, smaster);
+	if (ret)
+		return NULL;
+
+	return smaster;
+}
+EXPORT_SYMBOL_GPL(devm_siox_master_alloc);
+
+int siox_master_register(struct siox_master *smaster)
+{
+	int ret;
+
+	if (!siox_is_registered)
+		return -EPROBE_DEFER;
+
+	if (!smaster->pushpull)
+		return -EINVAL;
+
+	get_device(&smaster->dev);
+
+	dev_set_name(&smaster->dev, "siox-%d", smaster->busno);
+
+	mutex_init(&smaster->lock);
+	INIT_LIST_HEAD(&smaster->devices);
+
+	smaster->last_poll = jiffies;
+	smaster->poll_thread = kthread_run(siox_poll_thread, smaster,
+					   "siox-%d", smaster->busno);
+	if (IS_ERR(smaster->poll_thread)) {
+		smaster->active = 0;
+		return PTR_ERR(smaster->poll_thread);
+	}
+
+	ret = device_add(&smaster->dev);
+	if (ret)
+		kthread_stop(smaster->poll_thread);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(siox_master_register);
+
+void siox_master_unregister(struct siox_master *smaster)
+{
+	/* remove device */
+	device_del(&smaster->dev);
+
+	siox_master_lock(smaster);
+
+	__siox_stop(smaster);
+
+	while (smaster->num_devices) {
+		struct siox_device *sdevice;
+
+		sdevice = container_of(smaster->devices.prev,
+				       struct siox_device, node);
+		list_del(&sdevice->node);
+		smaster->num_devices--;
+
+		siox_master_unlock(smaster);
+
+		device_unregister(&sdevice->dev);
+
+		siox_master_lock(smaster);
+	}
+
+	siox_master_unlock(smaster);
+
+	put_device(&smaster->dev);
+}
+EXPORT_SYMBOL_GPL(siox_master_unregister);
+
+static void devm_siox_master_unregister(void *data)
+{
+	struct siox_master *smaster = data;
+
+	siox_master_unregister(smaster);
+}
+
+int devm_siox_master_register(struct device *dev, struct siox_master *smaster)
+{
+	int ret;
+
+	ret = siox_master_register(smaster);
+	if (ret)
+		return ret;
+
+	return devm_add_action_or_reset(dev, devm_siox_master_unregister, smaster);
+}
+EXPORT_SYMBOL_GPL(devm_siox_master_register);
+
+static struct siox_device *siox_device_add(struct siox_master *smaster,
+					   const char *type, size_t inbytes,
+					   size_t outbytes, u8 statustype)
+{
+	struct siox_device *sdevice;
+	int ret;
+	size_t buf_len;
+
+	sdevice = kzalloc_obj(*sdevice);
+	if (!sdevice)
+		return ERR_PTR(-ENOMEM);
+
+	sdevice->type = type;
+	sdevice->inbytes = inbytes;
+	sdevice->outbytes = outbytes;
+	sdevice->statustype = statustype;
+
+	sdevice->smaster = smaster;
+	sdevice->dev.parent = &smaster->dev;
+	sdevice->dev.bus = &siox_bus_type;
+	sdevice->dev.type = &siox_device_type;
+
+	siox_master_lock(smaster);
+
+	dev_set_name(&sdevice->dev, "siox-%d-%d",
+		     smaster->busno, smaster->num_devices);
+
+	buf_len = smaster->setbuf_len + inbytes +
+		smaster->getbuf_len + outbytes;
+	if (smaster->buf_len < buf_len) {
+		u8 *buf = krealloc(smaster->buf, buf_len, GFP_KERNEL);
+
+		if (!buf) {
+			dev_err(&smaster->dev,
+				"failed to realloc buffer to %zu\n", buf_len);
+			ret = -ENOMEM;
+			goto err_buf_alloc;
+		}
+
+		smaster->buf_len = buf_len;
+		smaster->buf = buf;
+	}
+
+	ret = device_register(&sdevice->dev);
+	if (ret) {
+		dev_err(&smaster->dev, "failed to register device: %d\n", ret);
+
+		goto err_device_register;
+	}
+
+	smaster->num_devices++;
+	list_add_tail(&sdevice->node, &smaster->devices);
+
+	smaster->setbuf_len += sdevice->inbytes;
+	smaster->getbuf_len += sdevice->outbytes;
+
+	sdevice->status_errors_kn = sysfs_get_dirent(sdevice->dev.kobj.sd,
+						     "status_errors");
+	sdevice->watchdog_kn = sysfs_get_dirent(sdevice->dev.kobj.sd,
+						"watchdog");
+	sdevice->watchdog_errors_kn = sysfs_get_dirent(sdevice->dev.kobj.sd,
+						       "watchdog_errors");
+	sdevice->connected_kn = sysfs_get_dirent(sdevice->dev.kobj.sd,
+						 "connected");
+
+	siox_master_unlock(smaster);
+
+	return sdevice;
+
+err_device_register:
+	/* don't care to make the buffer smaller again */
+	put_device(&sdevice->dev);
+	sdevice = NULL;
+
+err_buf_alloc:
+	siox_master_unlock(smaster);
+
+	kfree(sdevice);
+
+	return ERR_PTR(ret);
+}
+
+static void siox_device_remove(struct siox_master *smaster)
+{
+	struct siox_device *sdevice;
+
+	siox_master_lock(smaster);
+
+	if (!smaster->num_devices) {
+		siox_master_unlock(smaster);
+		return;
+	}
+
+	sdevice = container_of(smaster->devices.prev, struct siox_device, node);
+	list_del(&sdevice->node);
+	smaster->num_devices--;
+
+	smaster->setbuf_len -= sdevice->inbytes;
+	smaster->getbuf_len -= sdevice->outbytes;
+
+	if (!smaster->num_devices)
+		__siox_stop(smaster);
+
+	siox_master_unlock(smaster);
+
+	/*
+	 * This must be done without holding the master lock because we're
+	 * called from device_remove_store which also holds a sysfs mutex.
+	 * device_unregister tries to aquire the same lock.
+	 */
+	device_unregister(&sdevice->dev);
+}
+
+int __siox_driver_register(struct siox_driver *sdriver, struct module *owner)
+{
+	int ret;
+
+	if (unlikely(!siox_is_registered))
+		return -EPROBE_DEFER;
+
+	if (!sdriver->probe ||
+	    (!sdriver->set_data && !sdriver->get_data)) {
+		pr_err("Driver %s doesn't provide needed callbacks\n",
+		       sdriver->driver.name);
+		return -EINVAL;
+	}
+
+	sdriver->driver.owner = owner;
+	sdriver->driver.bus = &siox_bus_type;
+
+	ret = driver_register(&sdriver->driver);
+	if (ret)
+		pr_err("Failed to register siox driver %s (%d)\n",
+		       sdriver->driver.name, ret);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(__siox_driver_register);
+
+static int __init siox_init(void)
+{
+	int ret;
+
+	ret = bus_register(&siox_bus_type);
+	if (ret) {
+		pr_err("Registration of SIOX bus type failed: %d\n", ret);
+		return ret;
+	}
+
+	siox_is_registered = true;
+
+	return 0;
+}
+subsys_initcall(siox_init);
+
+static void __exit siox_exit(void)
+{
+	bus_unregister(&siox_bus_type);
+}
+module_exit(siox_exit);
+
+MODULE_AUTHOR("Uwe Kleine-Koenig <u.kleine-koenig@pengutronix.de>");
+MODULE_DESCRIPTION("Eckelmann SIOX driver core");
+MODULE_LICENSE("GPL v2");
diff --git a/drivers/siox/siox.h b/drivers/siox/siox.h
new file mode 100644
index 000000000..513f2c831
--- /dev/null
+++ b/drivers/siox/siox.h
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2015-2017 Pengutronix, Uwe Kleine-König <kernel@pengutronix.de>
+ */
+#include <linux/kernel.h>
+#include <linux/kthread.h>
+#include <linux/siox.h>
+
+#define to_siox_master(_dev)	container_of((_dev), struct siox_master, dev)
+struct siox_master {
+	/* these fields should be initialized by the driver */
+	int busno;
+	int (*pushpull)(struct siox_master *smaster,
+			size_t setbuf_len, const u8 setbuf[],
+			size_t getbuf_len, u8 getbuf[]);
+
+	/* might be initialized by the driver, if 0 it is set to HZ / 40 */
+	unsigned long poll_interval; /* in jiffies */
+
+	/* framework private stuff */
+	struct mutex lock;
+	bool active;
+	struct module *owner;
+	struct device dev;
+	unsigned int num_devices;
+	struct list_head devices;
+
+	size_t setbuf_len, getbuf_len;
+	size_t buf_len;
+	u8 *buf;
+	u8 status;
+
+	unsigned long last_poll;
+	struct task_struct *poll_thread;
+};
+
+static inline void *siox_master_get_devdata(struct siox_master *smaster)
+{
+	return dev_get_drvdata(&smaster->dev);
+}
+
+struct siox_master *siox_master_alloc(struct device *dev, size_t size);
+static inline void siox_master_put(struct siox_master *smaster)
+{
+	put_device(&smaster->dev);
+}
+
+struct siox_master *devm_siox_master_alloc(struct device *dev, size_t size);
+
+int siox_master_register(struct siox_master *smaster);
+void siox_master_unregister(struct siox_master *smaster);
+
+int devm_siox_master_register(struct device *dev, struct siox_master *smaster);