Add documentation for the uma/carveout_options and uma/carveout
attributes in sysfs

Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Yo-Jung Leo Lin (AMD) <Leo.Lin@amd.com>
---
 Documentation/gpu/amdgpu/driver-misc.rst   | 26 ++++++++++++++++++++++++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 29 +++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/Documentation/gpu/amdgpu/driver-misc.rst b/Documentation/gpu/amdgpu/driver-misc.rst
index 25b0c857816e..e1a964c3add2 100644
--- a/Documentation/gpu/amdgpu/driver-misc.rst
+++ b/Documentation/gpu/amdgpu/driver-misc.rst
@@ -128,3 +128,29 @@ smartshift_bias
 
 .. kernel-doc:: drivers/gpu/drm/amd/pm/amdgpu_pm.c
    :doc: smartshift_bias
+
+UMA Carveout
+============
+
+Some versions of Atom ROM expose available options for the VRAM carveout sizes,
+and allow changes to the carveout size via the ATCS function code 0xA on supported
+BIOS implementations.
+
+For those platforms, users can use the following files under uma/ to set the
+carveout size, in a way similar to what Windows users can do in the "Tuning"
+tab in AMD Adrenalin.
+
+Note that for BIOS implementations that don't support this, these files will not
+be created at all.
+
+uma/carveout_options
+--------------------
+
+.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+   :doc: uma/carveout_options
+
+uma/carveout
+--------------------
+
+.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+   :doc: uma/carveout
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index e78e6982312c..0271487e790c 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -418,6 +418,24 @@ static const struct attribute_group amdgpu_board_attrs_group = {
 	.is_visible = amdgpu_board_attrs_is_visible
 };
 
+/**
+ * DOC: uma/carveout_options
+ *
+ * This is a read-only file that lists all available UMA allocation
+ * options and their corresponding indices. Example output::
+ *
+ *     $ cat uma/carveout_options
+ *     0: Minimum (512 MB)
+ *     1:  (1 GB)
+ *     2:  (2 GB)
+ *     3:  (4 GB)
+ *     4:  (6 GB)
+ *     5:  (8 GB)
+ *     6:  (12 GB)
+ *     7: Medium (16 GB)
+ *     8:  (24 GB)
+ *     9: High (32 GB)
+ */
 static ssize_t carveout_options_show(struct device *dev,
 				     struct device_attribute *attr,
 				     char *buf)
@@ -450,6 +468,17 @@ static ssize_t carveout_options_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(carveout_options);
 
+/**
+ * DOC: uma/carveout
+ *
+ * This file is both readable and writable. When read, it shows the
+ * index of the current setting. Writing a valid index to this file
+ * allows users to change the UMA carveout size to the selected option
+ * on the next boot.
+ *
+ * The available options and their corresponding indices can be read
+ * from the uma/carveout_options file.
+ */
 static ssize_t carveout_show(struct device *dev,
 			     struct device_attribute *attr,
 			     char *buf)

-- 
2.43.0