[PATCH AUTOSEL 5.15 25/43] drm/amdgpu/gfx9: fix CSIB handling

[Sasha Levin]

From: Alex Deucher <alexander.deucher at amd.com>

[ Upstream commit a4a4c0ae6742ec7d6bf1548d2c6828de440814a0 ]

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

Reviewed-by: Rodrigo Siqueira <siqueira at igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---

Now I'll analyze the specific code changes and provide my backport
recommendation: **YES** This commit should be backported to stable
kernel trees. Here's my detailed analysis: ## Code Analysis The commit
fixes a logic bug in the `gfx_v9_0_get_csb_buffer()` function that
builds GPU command buffers for AMD GFX9 hardware. Looking at the code
change: **Before:** ```c 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; // ←
BUGGY early return } ``` **After:** ```c 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, execution continues ``` ## Why This Should Be Backported ### 1.
**Fixes a Clear Logic Bug** The early return prevents the function from
completing its work. After the loop, the function needs to write
critical termination packets: ```c buffer[count++] =
cpu_to_le32(PACKET3(PACKET3_PREAMBLE_CNTL, 0)); buffer[count++] =
cpu_to_le32(PACKET3_PREAMBLE_END_CLEAR_STATE); buffer[count++] =
cpu_to_le32(PACKET3(PACKET3_CLEAR_STATE, 0)); buffer[count++] =
cpu_to_le32(0); ``` ### 2. **Meets Stable Tree Criteria** - **Small and
contained**: Simple one-line removal with clear intent - **Low
regression risk**: Removing early return allows proper completion -
**Important bug fix**: Prevents GPU command buffer corruption - **No
architectural changes**: Pure bug fix without new features ### 3.
**Comparison with Historical Examples** Looking at the provided
historical commits, this fix is similar to commit #3 (marked YES) which
also fixed preamble handling. Both commits: - Fix logic bugs in AMD GPU
driver - Have minimal code changes - Address proper command/state
handling - Are critical for correct driver operation ### 4. **Stability
Impact** While currently masked because all existing clear state data
only uses `SECT_CONTEXT` sections, this bug creates: - **Buffer
corruption risk**: Incomplete command buffers sent to GPU - **Forward
compatibility issues**: Future hardware might use other section types -
**Inconsistent state**: Size calculation function has same bug pattern
### 5. **Hardware Criticality** This affects the GFX9 generation which
includes widely deployed GPUs like: - Vega series (RX Vega 56/64) -
Raven Ridge APUs (Ryzen 2000G/3000G series) - Renoir APUs (Ryzen 4000
series) ### 6. **Clear Commit Message** The commit message explicitly
states "We need to update the rest of the CSIB" - indicating this fixes
incomplete processing, exactly what stable backports target.
**Conclusion**: This is a textbook stable backport candidate - a small,
contained fix for a clear logic bug in a critical GPU initialization
path that could lead to hardware instability. The risk/reward ratio
strongly favors backporting.

 drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c b/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
index 811cacacc2090..6cc382197378d 100644
--- a/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
@@ -1782,8 +1782,6 @@ static void gfx_v9_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