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, 140 insertions, 0 deletions

diff --git a/drivers/leds/trigger/ledtrig-backlight.c b/drivers/leds/trigger/ledtrig-backlight.c
new file mode 100644
index 000000000..e67bc7c2a
--- /dev/null
+++ b/drivers/leds/trigger/ledtrig-backlight.c
@@ -0,0 +1,140 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Backlight emulation LED trigger
+ *
+ * Copyright 2008 (C) Rodolfo Giometti <giometti@linux.it>
+ * Copyright 2008 (C) Eurotech S.p.A. <info@eurotech.it>
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/leds.h>
+#include "../leds.h"
+
+#define BLANK		1
+#define UNBLANK		0
+
+struct bl_trig_notifier {
+	struct led_classdev *led;
+	int brightness;
+	int old_status;
+	unsigned invert;
+
+	struct list_head entry;
+};
+
+static DEFINE_MUTEX(ledtrig_backlight_list_mutex);
+static LIST_HEAD(ledtrig_backlight_list);
+
+static void ledtrig_backlight_notify_blank(struct bl_trig_notifier *n, int new_status)
+{
+	struct led_classdev *led = n->led;
+
+	if (new_status == n->old_status)
+		return;
+
+	if ((n->old_status == UNBLANK) ^ n->invert) {
+		n->brightness = led->brightness;
+		led_set_brightness_nosleep(led, LED_OFF);
+	} else {
+		led_set_brightness_nosleep(led, n->brightness);
+	}
+
+	n->old_status = new_status;
+}
+
+void ledtrig_backlight_blank(bool blank)
+{
+	struct bl_trig_notifier *n;
+	int new_status = blank ? BLANK : UNBLANK;
+
+	guard(mutex)(&ledtrig_backlight_list_mutex);
+
+	list_for_each_entry(n, &ledtrig_backlight_list, entry)
+		ledtrig_backlight_notify_blank(n, new_status);
+}
+EXPORT_SYMBOL(ledtrig_backlight_blank);
+
+static ssize_t bl_trig_invert_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct bl_trig_notifier *n = led_trigger_get_drvdata(dev);
+
+	return sprintf(buf, "%u\n", n->invert);
+}
+
+static ssize_t bl_trig_invert_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t num)
+{
+	struct led_classdev *led = led_trigger_get_led(dev);
+	struct bl_trig_notifier *n = led_trigger_get_drvdata(dev);
+	unsigned long invert;
+	int ret;
+
+	ret = kstrtoul(buf, 10, &invert);
+	if (ret < 0)
+		return ret;
+
+	if (invert > 1)
+		return -EINVAL;
+
+	n->invert = invert;
+
+	/* After inverting, we need to update the LED. */
+	if ((n->old_status == BLANK) ^ n->invert)
+		led_set_brightness_nosleep(led, LED_OFF);
+	else
+		led_set_brightness_nosleep(led, n->brightness);
+
+	return num;
+}
+static DEVICE_ATTR(inverted, 0644, bl_trig_invert_show, bl_trig_invert_store);
+
+static struct attribute *bl_trig_attrs[] = {
+	&dev_attr_inverted.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(bl_trig);
+
+static int bl_trig_activate(struct led_classdev *led)
+{
+	struct bl_trig_notifier *n;
+
+	n = kzalloc_obj(struct bl_trig_notifier);
+	if (!n)
+		return -ENOMEM;
+	led_set_trigger_data(led, n);
+
+	n->led = led;
+	n->brightness = led->brightness;
+	n->old_status = UNBLANK;
+
+	guard(mutex)(&ledtrig_backlight_list_mutex);
+	list_add(&n->entry, &ledtrig_backlight_list);
+
+	return 0;
+}
+
+static void bl_trig_deactivate(struct led_classdev *led)
+{
+	struct bl_trig_notifier *n = led_get_trigger_data(led);
+
+	guard(mutex)(&ledtrig_backlight_list_mutex);
+	list_del(&n->entry);
+
+	kfree(n);
+}
+
+static struct led_trigger bl_led_trigger = {
+	.name		= "backlight",
+	.activate	= bl_trig_activate,
+	.deactivate	= bl_trig_deactivate,
+	.groups		= bl_trig_groups,
+};
+module_led_trigger(bl_led_trigger);
+
+MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
+MODULE_DESCRIPTION("Backlight emulation LED trigger");
+MODULE_LICENSE("GPL v2");