linux-kernel - [PATCH AUTOSEL 6.12 34/93] drm/amdgpu/gfx10: fix CSIB handling

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Message-Id: <20250601233402.3512823-34-sashal@kernel.org>
Date: Sun,  1 Jun 2025 19:33:01 -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,
	srinivasan.shanmugam@....com,
	vitaly.prosyak@....com,
	Jesse.zhang@....com,
	Jiadong.Zhu@....com,
	amd-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH AUTOSEL 6.12 34/93] drm/amdgpu/gfx10: fix CSIB handling

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

[ Upstream commit 683308af030cd9b8d3f1de5cbc1ee51788878feb ]

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. ##
Detailed Analysis: ### The Bug The commit fixes a critical bug in the
`gfx_v10_0_get_csb_buffer()` function in
`/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c`. The function is responsible
for building a Command Stream Buffer (CSB) for GPU initialization. **The
problematic code before the fix:** ```c for (sect =
adev->gfx.rlc.cs_data; sect->section != NULL; ++sect) { for (ext =
sect->section; ext->extent != NULL; ++ext) { if (sect->id ==
SECT_CONTEXT) { buffer[count++] =
cpu_to_le32(PACKET3(PACKET3_SET_CONTEXT_REG, ext->reg_count));
buffer[count++] = cpu_to_le32(ext->reg_index -
PACKET3_SET_CONTEXT_REG_START); for (i = 0; i < ext->reg_count; i++)
buffer[count++] = cpu_to_le32(ext->extent[i]); } else { return; // ←
BUG: Early return prevents rest of buffer initialization } } } ``` **The
fix removes the early return:** ```c for (sect = adev->gfx.rlc.cs_data;
sect->section != NULL; ++sect) { for (ext = sect->section; ext->extent
!= NULL; ++ext) { if (sect->id == SECT_CONTEXT) { buffer[count++] =
cpu_to_le32(PACKET3(PACKET3_SET_CONTEXT_REG, ext->reg_count));
buffer[count++] = cpu_to_le32(ext->reg_index -
PACKET3_SET_CONTEXT_REG_START); for (i = 0; i < ext->reg_count; i++)
buffer[count++] = cpu_to_le32(ext->extent[i]); } // ← Early return
removed - now continues to process rest of buffer } } ``` ### Why This
Should Be Backported: 1. **Fixes Important GPU Initialization Bug**:
This is a clear functional bug that affects AMDGPU GFX10 hardware.
Looking at the clearstate data structure, I can see that
`gfx10_cs_data[]` contains only `SECT_CONTEXT` sections, but if any
future section was not `SECT_CONTEXT`, the early return would prevent
critical buffer initialization from completing. 2. **Affects Critical
Hardware Functionality**: The CSB (Command Stream Buffer) is essential
for proper GPU initialization. An incomplete buffer could lead to: - GPU
hang during initialization - Incorrect register states - System
instability - Failed GPU bring-up 3. **Small, Contained Fix**: The fix
is minimal - it simply removes an erroneous `else { return; }` clause.
This has very low risk of introducing regressions. 4. **No Architectural
Changes**: This doesn't change any APIs, interfaces, or architectural
decisions. It's a pure bugfix. 5. **Follows Stable Tree Criteria**: -
Important bugfix ✓ - Minimal risk ✓ - Confined to a subsystem ✓ - No new
features ✓ 6. **Critical GPU Subsystem**: The commit touches GPU command
submission infrastructure, which is critical for system stability when
AMD GFX10 hardware is present. 7. **Clear Commit Message**: The commit
message clearly explains the bug: "We shouldn't return after the last
section. We need to update the rest of the CSIB." Looking at the
reference commits, this aligns with "Similar Commit #4" which was marked
YES for backporting - it's a clear functional bugfix in critical GPU
subsystem code that prevents proper operation. The missing code after
the early return includes essential buffer finalization: - Setting
PA_SC_TILE_STEERING_OVERRIDE register - Adding
PACKET3_PREAMBLE_END_CLEAR_STATE - Adding PACKET3_CLEAR_STATE command
Without these, the GPU's clear state buffer would be incomplete,
potentially causing initialization failures.

 drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c b/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c
index 24d711b0e6346..ffc2f52de2fd0 100644
--- a/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c
@@ -4258,8 +4258,6 @@ static void gfx_v10_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