linux-kernel - [PATCH v2 2/2] Documentation/gpu: Add GFXOFF section

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Message-Id: <20220714191745.45512-2-andrealmeid@igalia.com>
Date:   Thu, 14 Jul 2022 16:17:45 -0300
From:   André Almeida <andrealmeid@...lia.com>
To:     Alex Deucher <alexander.deucher@....com>,
        'Christian König' <christian.koenig@....com>,
        'Pan Xinhui' <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Hawking Zhang <Hawking.Zhang@....com>,
        Tao Zhou <tao.zhou1@....com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Jack Xiao <Jack.Xiao@....com>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Tom St Denis <tom.stdenis@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>
Cc:     kernel-dev@...lia.com,
        André Almeida <andrealmeid@...lia.com>
Subject: [PATCH v2 2/2] Documentation/gpu: Add GFXOFF section

Add a GFXOFF section at "GPU Power Controls" file, explaining what it is
and how userspace can interact with it.

Signed-off-by: André Almeida <andrealmeid@...lia.com>
---
Changes from v1: file created

 Documentation/gpu/amdgpu/thermal.rst | 41 ++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/Documentation/gpu/amdgpu/thermal.rst b/Documentation/gpu/amdgpu/thermal.rst
index 8aeb0186c9ef..14c0fb874cf6 100644
--- a/Documentation/gpu/amdgpu/thermal.rst
+++ b/Documentation/gpu/amdgpu/thermal.rst
@@ -63,3 +63,44 @@ gpu_metrics
 
 .. kernel-doc:: drivers/gpu/drm/amd/pm/amdgpu_pm.c
    :doc: gpu_metrics
+
+GFXOFF
+======
+
+GFXOFF is a feature found in some mobile GPUs that saves power consumption. The
+card's firmware uses RLC (RunList Controller) to power off the gfx engine
+dynamically when there is no workload on gfx pipe and puts gfx into "idle"
+state. GFXOFF is on by default on supported GPUs.
+
+Userspace can interact with GFXOFF through a debugfs interface:
+
+``amdgpu_gfxoff``
+-----------------
+
+Use it to enable/disable GFXOFF, and to check if it's current enabled/disabled::
+
+  $ xxd -l1 -p /sys/kernel/debug/dri/0/amdgpu_gfxoff
+  01
+
+- Write 0 to disable it, and 1 to enable it.
+- Read 0 means it's disabled, 1 it's enabled.
+
+If it's enabled, that means that the GPU is free to enter into GFXOFF mode as
+needed. Disabled means that it will never enter GFXOFF mode.
+
+``amdgpu_gfxoff_status``
+------------------------
+
+Read it to check current GFXOFF's status of a GPU::
+
+  $ xxd -l1 -p /sys/kernel/debug/dri/0/amdgpu_gfxoff_status
+  02
+
+- 0: GPU is in GFXOFF state, the gfx engine is powered down.
+- 1: Transition out of GFXOFF state
+- 2: Not in GFXOFF state
+- 3: Transition into GFXOFF state
+
+If GFXOFF is enabled, the value will be transitioning around [0, 3], always
+getting into 0 when possible. When it's disabled, it's always at 2. Returns
+``-EINVAL`` if it's not supported.
-- 
2.37.0