From: Alex Deucher alexander.deucher@amd.com
[ Upstream commit 8307ebc15c1ea98a8a0b7837af1faa6c01514577 ]
We shouldn't return after the last section. We need to update the rest of the CSIB.
Reviewed-by: Rodrigo Siqueira siqueira@igalia.com Signed-off-by: Alex Deucher alexander.deucher@amd.com Signed-off-by: Sasha Levin sashal@kernel.org ---
Now let me understand what the bug is. Looking at the original code: ```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) { // process SECT_CONTEXT sections } else { return; // BUG: This returns early, skipping remaining code } } } // Important code that should always run: buffer[count++] = cpu_to_le32(PACKET3(PACKET3_SET_CONTEXT_REG, 1)); buffer[count++] = cpu_to_le32(mmPA_SC_RASTER_CONFIG - PACKET3_SET_CONTEXT_REG_START); // ... more important buffer initialization ``` The fix removes the early return so that all sections are processed and the important buffer initialization at the end always runs. **YES** This commit should be backported to stable kernel trees for the following reasons: 1. **Clear Bug Fix**: The commit fixes a clear logic error where an early return statement prevents critical buffer initialization code from executing. The original code would return immediately when encountering a non- SECT_CONTEXT section, skipping the important packet commands that should always be written to the buffer (PACKET3_SET_CONTEXT_REG, PACKET3_PREAMBLE_END_CLEAR_STATE, PACKET3_CLEAR_STATE). 2. **Functional Impact**: This bug affects the Clear State Indirect Buffer (CSIB) handling in AMD GPU driver for GFX6 hardware. The incomplete buffer initialization could lead to: - Incorrect GPU state during graphics operations - Potential rendering issues or GPU hangs - Inconsistent hardware behavior 3. **Small and Contained Fix**: The fix is minimal - it simply removes two lines (the else block with return statement). This is a low-risk change that doesn't introduce new functionality or alter the architecture. 4. **Hardware-Specific Bug**: This affects real users with GFX6 AMD GPUs. The bug prevents proper initialization of the GPU's clear state buffer, which is essential for correct GPU operation. 5. **Similar to Historical Backports**: Looking at commit 4 in the similar commits (marked as YES for backporting), which also fixed preamble handling issues in the AMD GPU driver, this follows a similar pattern of fixing command buffer handling bugs. The commit message clearly indicates this is a bug fix ("We shouldn't return after the last section. We need to update the rest of the CSIB"), and the code change confirms that critical buffer initialization was being skipped due to the premature return.
drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c | 2 -- 1 file changed, 2 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c b/drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c index 6a8dadea40f92..79074d22959b9 100644 --- a/drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c +++ b/drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c @@ -2897,8 +2897,6 @@ static void gfx_v6_0_get_csb_buffer(struct amdgpu_device *adev, buffer[count++] = cpu_to_le32(ext->reg_index - 0xa000); for (i = 0; i < ext->reg_count; i++) buffer[count++] = cpu_to_le32(ext->extent[i]); - } else { - return; } } }