On 2019-12-13 8:38, Yong Zhao wrote:
This prevents the NULL pointer access when there are fewer than 8 sdma
engines.

I don't see where you got a NULL pointer in the old code. Also this change is in an Arcturus-specific source file. AFAIK Arcturus always has 8 SDMA engines.

The new code is much longer than the old code. I don't see how that's an improvement. See one more comment inline.



Change-Id: Iabae9bff7546b344720905d5d4a5cfc066a79d25
Signed-off-by: Yong Zhao <yong.z...@amd.com>
---
  .../drm/amd/amdgpu/amdgpu_amdkfd_arcturus.c   | 64 ++++++++++++-------
  1 file changed, 42 insertions(+), 22 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_arcturus.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_arcturus.c
index 3c119407dc34..2ad088f10493 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_arcturus.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_arcturus.c
@@ -71,32 +71,52 @@ static uint32_t get_sdma_rlc_reg_offset(struct 
amdgpu_device *adev,
                                unsigned int engine_id,
                                unsigned int queue_id)
  {
-       uint32_t sdma_engine_reg_base[8] = {
-               SOC15_REG_OFFSET(SDMA0, 0,
-                                mmSDMA0_RLC0_RB_CNTL) - mmSDMA0_RLC0_RB_CNTL,
-               SOC15_REG_OFFSET(SDMA1, 0,
-                                mmSDMA1_RLC0_RB_CNTL) - mmSDMA1_RLC0_RB_CNTL,
-               SOC15_REG_OFFSET(SDMA2, 0,
-                                mmSDMA2_RLC0_RB_CNTL) - mmSDMA2_RLC0_RB_CNTL,
-               SOC15_REG_OFFSET(SDMA3, 0,
-                                mmSDMA3_RLC0_RB_CNTL) - mmSDMA3_RLC0_RB_CNTL,
-               SOC15_REG_OFFSET(SDMA4, 0,
-                                mmSDMA4_RLC0_RB_CNTL) - mmSDMA4_RLC0_RB_CNTL,
-               SOC15_REG_OFFSET(SDMA5, 0,
-                                mmSDMA5_RLC0_RB_CNTL) - mmSDMA5_RLC0_RB_CNTL,
-               SOC15_REG_OFFSET(SDMA6, 0,
-                                mmSDMA6_RLC0_RB_CNTL) - mmSDMA6_RLC0_RB_CNTL,
-               SOC15_REG_OFFSET(SDMA7, 0,
-                                mmSDMA7_RLC0_RB_CNTL) - mmSDMA7_RLC0_RB_CNTL
-       };
-
-       uint32_t retval = sdma_engine_reg_base[engine_id]

I'm not sure where you were getting a NULL pointer, but I guess this could have used a range check to make sure engine_id is < 8 before indexing into the array. The equivalent in the switch statement would be a default case. See below.


+       uint32_t sdma_engine_reg_base;
+       uint32_t sdma_rlc_reg_offset;
+
+       switch (engine_id) {
+       case 0:
+               sdma_engine_reg_base = SOC15_REG_OFFSET(SDMA0, 0,
+                               mmSDMA0_RLC0_RB_CNTL) - mmSDMA0_RLC0_RB_CNTL;
+               break;
+       case 1:
+               sdma_engine_reg_base = SOC15_REG_OFFSET(SDMA1, 0,
+                               mmSDMA1_RLC0_RB_CNTL) - mmSDMA1_RLC0_RB_CNTL;
+               break;
+       case 2:
+               sdma_engine_reg_base = SOC15_REG_OFFSET(SDMA2, 0,
+                               mmSDMA2_RLC0_RB_CNTL) - mmSDMA2_RLC0_RB_CNTL;
+               break;
+       case 3:
+               sdma_engine_reg_base = SOC15_REG_OFFSET(SDMA3, 0,
+                               mmSDMA3_RLC0_RB_CNTL) - mmSDMA3_RLC0_RB_CNTL;
+               break;
+       case 4:
+               sdma_engine_reg_base = SOC15_REG_OFFSET(SDMA4, 0,
+                               mmSDMA4_RLC0_RB_CNTL) - mmSDMA4_RLC0_RB_CNTL;
+               break;
+       case 5:
+               sdma_engine_reg_base = SOC15_REG_OFFSET(SDMA5, 0,
+                               mmSDMA5_RLC0_RB_CNTL) - mmSDMA5_RLC0_RB_CNTL;
+               break;
+       case 6:
+               sdma_engine_reg_base = SOC15_REG_OFFSET(SDMA6, 0,
+                               mmSDMA6_RLC0_RB_CNTL) - mmSDMA6_RLC0_RB_CNTL;
+               break;
+       case 7:
+               sdma_engine_reg_base = SOC15_REG_OFFSET(SDMA7, 0,
+                               mmSDMA7_RLC0_RB_CNTL) - mmSDMA7_RLC0_RB_CNTL;
+               break;
+

Do you need a default case for the switch statement? I think you get a compiler warning without one.

Regards,
  Felix


+       }
+
+       sdma_rlc_reg_offset = sdma_engine_reg_base
                + queue_id * (mmSDMA0_RLC1_RB_CNTL - mmSDMA0_RLC0_RB_CNTL);
pr_debug("RLC register offset for SDMA%d RLC%d: 0x%x\n", engine_id,
-                       queue_id, retval);
+                       queue_id, sdma_rlc_reg_offset);
- return retval;
+       return sdma_rlc_reg_offset;
  }
static int kgd_hqd_sdma_load(struct kgd_dev *kgd, void *mqd,
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