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)

1 files changed, 141 insertions, 0 deletions

diff --git a/drivers/pps/clients/pps-ldisc.c b/drivers/pps/clients/pps-ldisc.c
new file mode 100644
index 000000000..fa5660f3c
--- /dev/null
+++ b/drivers/pps/clients/pps-ldisc.c
@@ -0,0 +1,141 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * pps-ldisc.c -- PPS line discipline
+ *
+ * Copyright (C) 2008	Rodolfo Giometti <giometti@linux.it>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/serial_core.h>
+#include <linux/tty.h>
+#include <linux/pps_kernel.h>
+#include <linux/bug.h>
+
+static void pps_tty_dcd_change(struct tty_struct *tty, bool active)
+{
+	struct pps_device *pps;
+	struct pps_event_time ts;
+
+	pps_get_ts(&ts);
+
+	pps = pps_lookup_dev(tty);
+	/*
+	 * This should never fail, but the ldisc locking is very
+	 * convoluted, so don't crash just in case.
+	 */
+	if (WARN_ON_ONCE(pps == NULL))
+		return;
+
+	/* Now do the PPS event report */
+	pps_event(pps, &ts, active ? PPS_CAPTUREASSERT :
+			PPS_CAPTURECLEAR, NULL);
+
+	dev_dbg(&pps->dev, "PPS %s at %lu\n",
+			active ? "assert" : "clear", jiffies);
+}
+
+static int (*alias_n_tty_open)(struct tty_struct *tty);
+
+static int pps_tty_open(struct tty_struct *tty)
+{
+	struct pps_source_info info;
+	struct tty_driver *drv = tty->driver;
+	int index = tty->index + drv->name_base;
+	struct pps_device *pps;
+	int ret;
+
+	info.owner = THIS_MODULE;
+	info.dev = NULL;
+	snprintf(info.name, PPS_MAX_NAME_LEN, "%s%d", drv->driver_name, index);
+	snprintf(info.path, PPS_MAX_NAME_LEN, "/dev/%s%d", drv->name, index);
+	info.mode = PPS_CAPTUREBOTH | \
+			PPS_OFFSETASSERT | PPS_OFFSETCLEAR | \
+			PPS_CANWAIT | PPS_TSFMT_TSPEC;
+
+	pps = pps_register_source(&info, PPS_CAPTUREBOTH | \
+				PPS_OFFSETASSERT | PPS_OFFSETCLEAR);
+	if (IS_ERR(pps)) {
+		pr_err("cannot register PPS source \"%s\"\n", info.path);
+		return PTR_ERR(pps);
+	}
+	pps->lookup_cookie = tty;
+
+	/* Now open the base class N_TTY ldisc */
+	ret = alias_n_tty_open(tty);
+	if (ret < 0) {
+		pr_err("cannot open tty ldisc \"%s\"\n", info.path);
+		goto err_unregister;
+	}
+
+	dev_dbg(&pps->dev, "source \"%s\" added\n", info.path);
+
+	return 0;
+
+err_unregister:
+	pps_unregister_source(pps);
+	return ret;
+}
+
+static void (*alias_n_tty_close)(struct tty_struct *tty);
+
+static void pps_tty_close(struct tty_struct *tty)
+{
+	struct pps_device *pps = pps_lookup_dev(tty);
+
+	alias_n_tty_close(tty);
+
+	if (WARN_ON(!pps))
+		return;
+
+	dev_info(&pps->dev, "removed\n");
+	pps_unregister_source(pps);
+}
+
+static struct tty_ldisc_ops pps_ldisc_ops;
+
+/*
+ * Module stuff
+ */
+
+static int __init pps_tty_init(void)
+{
+	int err;
+
+	/* Inherit the N_TTY's ops */
+	n_tty_inherit_ops(&pps_ldisc_ops);
+
+	/* Save N_TTY's open()/close() methods */
+	alias_n_tty_open = pps_ldisc_ops.open;
+	alias_n_tty_close = pps_ldisc_ops.close;
+
+	/* Init PPS_TTY data */
+	pps_ldisc_ops.owner = THIS_MODULE;
+	pps_ldisc_ops.num = N_PPS;
+	pps_ldisc_ops.name = "pps_tty";
+	pps_ldisc_ops.dcd_change = pps_tty_dcd_change;
+	pps_ldisc_ops.open = pps_tty_open;
+	pps_ldisc_ops.close = pps_tty_close;
+
+	err = tty_register_ldisc(&pps_ldisc_ops);
+	if (err)
+		pr_err("can't register PPS line discipline\n");
+	else
+		pr_info("PPS line discipline registered\n");
+
+	return err;
+}
+
+static void __exit pps_tty_cleanup(void)
+{
+	tty_unregister_ldisc(&pps_ldisc_ops);
+}
+
+module_init(pps_tty_init);
+module_exit(pps_tty_cleanup);
+
+MODULE_ALIAS_LDISC(N_PPS);
+MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
+MODULE_DESCRIPTION("PPS TTY device driver");
+MODULE_LICENSE("GPL");