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, 156 insertions, 0 deletions

diff --git a/Documentation/i2c/functionality.rst b/Documentation/i2c/functionality.rst
new file mode 100644
index 000000000..377507c56
--- /dev/null
+++ b/Documentation/i2c/functionality.rst
@@ -0,0 +1,156 @@
+=======================
+I2C/SMBus Functionality
+=======================
+
+INTRODUCTION
+------------
+
+Because not every I2C or SMBus adapter implements everything in the
+I2C specifications, a client can not trust that everything it needs
+is implemented when it is given the option to attach to an adapter:
+the client needs some way to check whether an adapter has the needed
+functionality.
+
+
+FUNCTIONALITY CONSTANTS
+-----------------------
+
+For the most up-to-date list of functionality constants, please check
+<uapi/linux/i2c.h>!
+
+  =============================== ==============================================
+  I2C_FUNC_I2C                    Plain i2c-level commands (Pure SMBus
+                                  adapters typically can not do these)
+  I2C_FUNC_10BIT_ADDR             Handles the 10-bit address extensions
+  I2C_FUNC_PROTOCOL_MANGLING      Knows about the I2C_M_IGNORE_NAK,
+                                  I2C_M_REV_DIR_ADDR and I2C_M_NO_RD_ACK
+                                  flags (which modify the I2C protocol!)
+  I2C_FUNC_NOSTART                Can skip repeated start sequence
+  I2C_FUNC_SMBUS_QUICK            Handles the SMBus write_quick command
+  I2C_FUNC_SMBUS_READ_BYTE        Handles the SMBus read_byte command
+  I2C_FUNC_SMBUS_WRITE_BYTE       Handles the SMBus write_byte command
+  I2C_FUNC_SMBUS_READ_BYTE_DATA   Handles the SMBus read_byte_data command
+  I2C_FUNC_SMBUS_WRITE_BYTE_DATA  Handles the SMBus write_byte_data command
+  I2C_FUNC_SMBUS_READ_WORD_DATA   Handles the SMBus read_word_data command
+  I2C_FUNC_SMBUS_WRITE_WORD_DATA  Handles the SMBus write_byte_data command
+  I2C_FUNC_SMBUS_PROC_CALL        Handles the SMBus process_call command
+  I2C_FUNC_SMBUS_READ_BLOCK_DATA  Handles the SMBus read_block_data command
+  I2C_FUNC_SMBUS_WRITE_BLOCK_DATA Handles the SMBus write_block_data command
+  I2C_FUNC_SMBUS_READ_I2C_BLOCK   Handles the SMBus read_i2c_block_data command
+  I2C_FUNC_SMBUS_WRITE_I2C_BLOCK  Handles the SMBus write_i2c_block_data command
+  =============================== ==============================================
+
+A few combinations of the above flags are also defined for your convenience:
+
+  =========================       ======================================
+  I2C_FUNC_SMBUS_BYTE             Handles the SMBus read_byte
+                                  and write_byte commands
+  I2C_FUNC_SMBUS_BYTE_DATA        Handles the SMBus read_byte_data
+                                  and write_byte_data commands
+  I2C_FUNC_SMBUS_WORD_DATA        Handles the SMBus read_word_data
+                                  and write_word_data commands
+  I2C_FUNC_SMBUS_BLOCK_DATA       Handles the SMBus read_block_data
+                                  and write_block_data commands
+  I2C_FUNC_SMBUS_I2C_BLOCK        Handles the SMBus read_i2c_block_data
+                                  and write_i2c_block_data commands
+  I2C_FUNC_SMBUS_EMUL             Handles all SMBus commands that can be
+                                  emulated by a real I2C adapter (using
+                                  the transparent emulation layer)
+  =========================       ======================================
+
+In kernel versions prior to 3.5 I2C_FUNC_NOSTART was implemented as
+part of I2C_FUNC_PROTOCOL_MANGLING.
+
+
+ADAPTER IMPLEMENTATION
+----------------------
+
+When you write a new adapter driver, you will have to implement a
+function callback ``functionality``. Typical implementations are given
+below.
+
+A typical SMBus-only adapter would list all the SMBus transactions it
+supports. This example comes from the i2c-piix4 driver::
+
+  static u32 piix4_func(struct i2c_adapter *adapter)
+  {
+	return I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_BYTE |
+	       I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA |
+	       I2C_FUNC_SMBUS_BLOCK_DATA;
+  }
+
+A typical full-I2C adapter would use the following (from the i2c-pxa
+driver)::
+
+  static u32 i2c_pxa_functionality(struct i2c_adapter *adap)
+  {
+	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
+  }
+
+I2C_FUNC_SMBUS_EMUL includes all the SMBus transactions (with the
+addition of I2C block transactions) which i2c-core can emulate using
+I2C_FUNC_I2C without any help from the adapter driver. The idea is
+to let the client drivers check for the support of SMBus functions
+without having to care whether the said functions are implemented in
+hardware by the adapter, or emulated in software by i2c-core on top
+of an I2C adapter.
+
+
+CLIENT CHECKING
+---------------
+
+Before a client tries to attach to an adapter, or even do tests to check
+whether one of the devices it supports is present on an adapter, it should
+check whether the needed functionality is present. The typical way to do
+this is (from the lm75 driver)::
+
+  static int lm75_detect(...)
+  {
+	(...)
+	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA |
+				     I2C_FUNC_SMBUS_WORD_DATA))
+		goto exit;
+	(...)
+  }
+
+Here, the lm75 driver checks if the adapter can do both SMBus byte data
+and SMBus word data transactions. If not, then the driver won't work on
+this adapter and there's no point in going on. If the check above is
+successful, then the driver knows that it can call the following
+functions: i2c_smbus_read_byte_data(), i2c_smbus_write_byte_data(),
+i2c_smbus_read_word_data() and i2c_smbus_write_word_data(). As a rule of
+thumb, the functionality constants you test for with
+i2c_check_functionality() should match exactly the i2c_smbus_* functions
+which you driver is calling.
+
+Note that the check above doesn't tell whether the functionalities are
+implemented in hardware by the underlying adapter or emulated in
+software by i2c-core. Client drivers don't have to care about this, as
+i2c-core will transparently implement SMBus transactions on top of I2C
+adapters.
+
+
+CHECKING THROUGH /DEV
+---------------------
+
+If you try to access an adapter from a userspace program, you will have
+to use the /dev interface. You will still have to check whether the
+functionality you need is supported, of course. This is done using
+the I2C_FUNCS ioctl. An example, adapted from the i2cdetect program, is
+below::
+
+  int file;
+  if (file = open("/dev/i2c-0", O_RDWR) < 0) {
+	/* Some kind of error handling */
+	exit(1);
+  }
+  if (ioctl(file, I2C_FUNCS, &funcs) < 0) {
+	/* Some kind of error handling */
+	exit(1);
+  }
+  if (!(funcs & I2C_FUNC_SMBUS_QUICK)) {
+	/* Oops, the needed functionality (SMBus write_quick function) is
+           not available! */
+	exit(1);
+  }
+  /* Now it is safe to use the SMBus write_quick command */