linux-kernel - [PATCH AUTOSEL 6.14 021/102] drm/amdgpu/gfx11: fix CSIB handling

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Message-Id: <20250601232937.3510379-21-sashal@kernel.org>
Date: Sun,  1 Jun 2025 19:28:13 -0400
From: Sasha Levin <sashal@...nel.org>
To: patches@...ts.linux.dev,
	stable@...r.kernel.org
Cc: Alex Deucher <alexander.deucher@....com>,
	Rodrigo Siqueira <siqueira@...lia.com>,
	Sasha Levin <sashal@...nel.org>,
	christian.koenig@....com,
	airlied@...il.com,
	simona@...ll.ch,
	sunil.khatri@....com,
	vitaly.prosyak@....com,
	srinivasan.shanmugam@....com,
	tim.huang@....com,
	Prike.Liang@....com,
	Jesse.zhang@....com,
	amd-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH AUTOSEL 6.14 021/102] drm/amdgpu/gfx11: fix CSIB handling

From: Alex Deucher <alexander.deucher@....com>

[ Upstream commit a9a8bccaa3ba64d509cf7df387cf0b5e1cd06499 ]

We shouldn't return after the last section.
We need to update the rest of the CSIB.

Reviewed-by: Rodrigo Siqueira <siqueira@...lia.com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---

**YES** This commit should be backported to stable kernel trees. ##
Analysis ### Code Change Analysis The commit fixes a **critical bug in
CSIB (Clear State Init Buffer) handling** in the GFX11 AMD GPU driver.
The problematic code in `gfx_v11_0_get_csb_buffer()` at line 861
contained: ```c } else { return; // This was the bug! } ``` This early
return statement prevented the function from completing the CSIB setup
when encountering non-SECT_CONTEXT sections. The fix removes this
premature return, allowing the function to continue and properly
complete the buffer initialization with: 1.
**PA_SC_TILE_STEERING_OVERRIDE register setup** (lines 866-870) 2.
**PACKET3_PREAMBLE_END_CLEAR_STATE** (lines 872-873) 3.
**PACKET3_CLEAR_STATE** (lines 875-876) ### Why This Qualifies for
Backporting 1. **Fixes Important Hardware Initialization Bug**: CSIB is
critical for GPU state management. Incomplete initialization can cause
GPU hangs, rendering artifacts, or system instability. 2. **Small,
Contained Fix**: The change removes only 2 lines (`} else { return; }`)
- minimal and low-risk. 3. **No Architectural Changes**: This is a pure
bugfix with no new features or major code restructuring. 4. **Critical
Subsystem**: Graphics drivers are essential for system functionality,
and GPU state corruption can cause severe user-visible issues. 5.
**Pattern Consistency**: Looking at similar sections across different
GFX versions (v10, v9, etc.), they all handle non-SECT_CONTEXT sections
by continuing rather than returning early, confirming this was indeed a
bug. ### Historical Context Support From examining the codebase, this
pattern is consistent across all GFX generations: - **gfx_v10_0.c:4227**
and **gfx_v10_0.c:4266**: Handle SECT_CONTEXT but continue for other
sections - **gfx_v9_0.c:1609** and **gfx_v9_0.c:1645**: Same pattern -
**gfx_v8_0.c**, **gfx_v7_0.c**, **gfx_v6_0.c**: All follow the same
approach The previous GFX10 CSIB fix (commit 4905880b4515) shows AMD's
commitment to ensuring proper CSIB initialization across GPU
generations, reinforcing the importance of this subsystem. ### Risk
Assessment - **Regression Risk**: Extremely low - only removes incorrect
early termination - **Testing Surface**: Affects GFX11 GPU
initialization, easily testable - **Side Effects**: None - only allows
completion of intended initialization sequence This is a textbook
example of a stable-worthy fix: important bug, minimal change, no
regression risk, and affects critical hardware functionality.

 drivers/gpu/drm/amd/amdgpu/gfx_v11_0.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v11_0.c b/drivers/gpu/drm/amd/amdgpu/gfx_v11_0.c
index e050c2e4ea734..a1a49042e6152 100644
--- a/drivers/gpu/drm/amd/amdgpu/gfx_v11_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/gfx_v11_0.c
@@ -857,8 +857,6 @@ static void gfx_v11_0_get_csb_buffer(struct amdgpu_device *adev,
 						PACKET3_SET_CONTEXT_REG_START);
 				for (i = 0; i < ext->reg_count; i++)
 					buffer[count++] = cpu_to_le32(ext->extent[i]);
-			} else {
-				return;
 			}
 		}
 	}
-- 
2.39.5