From: Alex Deucher alexander.deucher@amd.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@igalia.com Signed-off-by: Alex Deucher alexander.deucher@amd.com Signed-off-by: Sasha Levin sashal@kernel.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 a84deb3c79a30..44380923b01c8 100644 --- a/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c +++ b/drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c @@ -944,8 +944,6 @@ 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; } } }