linux-kernel - [PATCH v2 5/5] Documentation/amdgpu: Add UMA carveout details

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Message-ID: <20251114-vram-carveout-tuning-for-upstream-v2-5-4f6bdd48030d@amd.com>
Date: Fri, 14 Nov 2025 16:42:25 +0800
From: "Yo-Jung Leo Lin (AMD)" <Leo.Lin@....com>
To: Alex Deucher <alexander.deucher@....com>, Christian König
	<christian.koenig@....com>, David Airlie <airlied@...il.com>, Simona Vetter
	<simona@...ll.ch>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
	Jonathan Corbet <corbet@....net>
CC: <amd-gfx@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
	<linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>, "Tsao, Anson"
	<anson.tsao@....com>, "Mario Limonciello (AMD) (kernel.org)"
	<superm1@...nel.org>, "Yo-Jung Leo Lin (AMD)" <Leo.Lin@....com>
Subject: [PATCH v2 5/5] Documentation/amdgpu: Add UMA carveout details

Add documentation for the uma_carveout_options and uma_carveout
attributes in sysfs

Signed-off-by: Yo-Jung Leo Lin (AMD) <Leo.Lin@....com>
---
 Documentation/gpu/amdgpu/driver-misc.rst | 26 ++++++++++++++++++++++++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.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..afefab4fa0ac 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 file 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_acpi.c
+   :doc: uma_carveout_options
+
+uma_carveout
+--------------------
+
+.. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
+   :doc: uma_carveout
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
index b9378f34eb79..10cc6bf28a0f 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
@@ -1248,6 +1248,24 @@ int amdgpu_acpi_get_mem_info(struct amdgpu_device *adev, int xcc_id,
 	return -ENOENT;
 }
 
+/**
+ * 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 (0 GB)
+ *     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 uma_carveout_options_show(struct device *dev,
 					 struct device_attribute *attr,
 					 char *buf)
@@ -1269,6 +1287,17 @@ static ssize_t uma_carveout_options_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(uma_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 uma_carveout_show(struct device *dev,
 				 struct device_attribute *attr,
 				 char *buf)

-- 
2.43.0