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)

2 files changed, 166 insertions, 0 deletions

diff --git a/samples/hung_task/Makefile b/samples/hung_task/Makefile
new file mode 100644
index 000000000..86036f1a2
--- /dev/null
+++ b/samples/hung_task/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_tests.o
diff --git a/samples/hung_task/hung_task_tests.c b/samples/hung_task/hung_task_tests.c
new file mode 100644
index 000000000..0360ec916
--- /dev/null
+++ b/samples/hung_task/hung_task_tests.c
@@ -0,0 +1,164 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * hung_task_tests.c - Sample code for testing hung tasks with mutex,
+ * semaphore, etc.
+ *
+ * Usage: Load this module and read `<debugfs>/hung_task/mutex`,
+ *        `<debugfs>/hung_task/semaphore`, `<debugfs>/hung_task/rw_semaphore_read`,
+ *        `<debugfs>/hung_task/rw_semaphore_write`, etc., with 2 or more processes.
+ *
+ * This is for testing kernel hung_task error messages with various locking
+ * mechanisms (e.g., mutex, semaphore, rw_semaphore_read, rw_semaphore_write, etc.).
+ * Note that this may freeze your system or cause a panic. Use only for testing purposes.
+ */
+
+#include <linux/debugfs.h>
+#include <linux/delay.h>
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/semaphore.h>
+#include <linux/rwsem.h>
+
+#define HUNG_TASK_DIR			"hung_task"
+#define HUNG_TASK_MUTEX_FILE		"mutex"
+#define HUNG_TASK_SEM_FILE		"semaphore"
+#define HUNG_TASK_RWSEM_READ_FILE	"rw_semaphore_read"
+#define HUNG_TASK_RWSEM_WRITE_FILE	"rw_semaphore_write"
+#define SLEEP_SECOND			256
+
+static const char dummy_string[] = "This is a dummy string.";
+static DEFINE_MUTEX(dummy_mutex);
+static DEFINE_SEMAPHORE(dummy_sem, 1);
+static DECLARE_RWSEM(dummy_rwsem);
+static struct dentry *hung_task_dir;
+
+/* Mutex-based read function */
+static ssize_t read_dummy_mutex(struct file *file, char __user *user_buf,
+				size_t count, loff_t *ppos)
+{
+	/* Check if data is already read */
+	if (*ppos >= sizeof(dummy_string))
+		return 0;
+
+	/* Second task waits on mutex, entering uninterruptible sleep */
+	guard(mutex)(&dummy_mutex);
+
+	/* First task sleeps here, interruptible */
+	msleep_interruptible(SLEEP_SECOND * 1000);
+
+	return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
+				       sizeof(dummy_string));
+}
+
+/* Semaphore-based read function */
+static ssize_t read_dummy_semaphore(struct file *file, char __user *user_buf,
+				    size_t count, loff_t *ppos)
+{
+	/* Check if data is already read */
+	if (*ppos >= sizeof(dummy_string))
+		return 0;
+
+	/* Second task waits on semaphore, entering uninterruptible sleep */
+	down(&dummy_sem);
+
+	/* First task sleeps here, interruptible */
+	msleep_interruptible(SLEEP_SECOND * 1000);
+
+	up(&dummy_sem);
+
+	return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
+				       sizeof(dummy_string));
+}
+
+/* Read-write semaphore read function */
+static ssize_t read_dummy_rwsem_read(struct file *file, char __user *user_buf,
+				     size_t count, loff_t *ppos)
+{
+	/* Check if data is already read */
+	if (*ppos >= sizeof(dummy_string))
+		return 0;
+
+	/* Acquires read lock, allowing concurrent readers but blocks if write lock is held */
+	down_read(&dummy_rwsem);
+
+	/* Sleeps here, potentially triggering hung task detection if lock is held too long */
+	msleep_interruptible(SLEEP_SECOND * 1000);
+
+	up_read(&dummy_rwsem);
+
+	return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
+				       sizeof(dummy_string));
+}
+
+/* Read-write semaphore write function */
+static ssize_t read_dummy_rwsem_write(struct file *file, char __user *user_buf,
+				      size_t count, loff_t *ppos)
+{
+	/* Check if data is already read */
+	if (*ppos >= sizeof(dummy_string))
+		return 0;
+
+	/* Acquires exclusive write lock, blocking all other readers and writers */
+	down_write(&dummy_rwsem);
+
+	/* Sleeps here, potentially triggering hung task detection if lock is held too long */
+	msleep_interruptible(SLEEP_SECOND * 1000);
+
+	up_write(&dummy_rwsem);
+
+	return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
+				       sizeof(dummy_string));
+}
+
+/* File operations for mutex */
+static const struct file_operations hung_task_mutex_fops = {
+	.read = read_dummy_mutex,
+};
+
+/* File operations for semaphore */
+static const struct file_operations hung_task_sem_fops = {
+	.read = read_dummy_semaphore,
+};
+
+/* File operations for rw_semaphore read */
+static const struct file_operations hung_task_rwsem_read_fops = {
+	.read = read_dummy_rwsem_read,
+};
+
+/* File operations for rw_semaphore write */
+static const struct file_operations hung_task_rwsem_write_fops = {
+	.read = read_dummy_rwsem_write,
+};
+
+static int __init hung_task_tests_init(void)
+{
+	hung_task_dir = debugfs_create_dir(HUNG_TASK_DIR, NULL);
+	if (IS_ERR(hung_task_dir))
+		return PTR_ERR(hung_task_dir);
+
+	/* Create debugfs files for mutex and semaphore tests */
+	debugfs_create_file(HUNG_TASK_MUTEX_FILE, 0400, hung_task_dir, NULL,
+			    &hung_task_mutex_fops);
+	debugfs_create_file(HUNG_TASK_SEM_FILE, 0400, hung_task_dir, NULL,
+			    &hung_task_sem_fops);
+	debugfs_create_file(HUNG_TASK_RWSEM_READ_FILE, 0400, hung_task_dir, NULL,
+			    &hung_task_rwsem_read_fops);
+	debugfs_create_file(HUNG_TASK_RWSEM_WRITE_FILE, 0400, hung_task_dir, NULL,
+			    &hung_task_rwsem_write_fops);
+
+	return 0;
+}
+
+static void __exit hung_task_tests_exit(void)
+{
+	debugfs_remove_recursive(hung_task_dir);
+}
+
+module_init(hung_task_tests_init);
+module_exit(hung_task_tests_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Masami Hiramatsu <mhiramat@kernel.org>");
+MODULE_AUTHOR("Zi Li <amaindex@outlook.com>");
+MODULE_DESCRIPTION("Simple sleep under lock files for testing hung task");