Re: [PATCH 1/1] drm/amdkfd: Fix unaligned doorbell absolute offset for gfx8

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On 27/09/2023 19:27, Felix Kuehling wrote:

[+Mukul]

On 2023-09-27 12:16, Arvind Yadav wrote:
This patch is to adjust the absolute doorbell offset
against the doorbell id considering the doorbell
size of 32/64 bit.

Cc: Christian Koenig<christian.koenig@xxxxxxx>
Cc: Alex Deucher<alexander.deucher@xxxxxxx>
Signed-off-by: Shashank Sharma<shashank.sharma@xxxxxxx>
Signed-off-by: Arvind Yadav<Arvind.Yadav@xxxxxxx>
---
  drivers/gpu/drm/amd/amdkfd/kfd_device_queue_manager.c | 11 ++++++++++-
  1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_device_queue_manager.c b/drivers/gpu/drm/amd/amdkfd/kfd_device_queue_manager.c
index 0d3d538b64eb..c327f7f604d7 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_device_queue_manager.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_device_queue_manager.c
@@ -407,7 +407,16 @@ static int allocate_doorbell(struct qcm_process_device *qpd,
q->properties.doorbell_off = amdgpu_doorbell_index_on_bar(dev->adev,
  								  qpd->proc_doorbells,
-								  q->doorbell_id);
+								  0);

Looks like we're now always calling amdgpu_doorbell_index_on_bar with the third parameter = 0. So we could remove that parameter. It doesn't do us any good and only causes bugs if we use any non-0 value.

Hey Felix,

Actually this was happening because in usermode KFD library the doorbell-size is for non-SOC15() hardware is hard coded to 4 bytes.

We added this fix just so that the library code doesn't need to be changed, but can still get aligned to kernel code.

GFX Usermode queue code uses this doorbell-index parameter, and it gives us the right offset.


Regards

Shashank


+
+	/* Adjust the absolute doorbell offset against the doorbell id considering
+	 * the doorbell size of 32/64 bit.
+	 */
+	if (!KFD_IS_SOC15(dev))
+		q->properties.doorbell_off += q->doorbell_id;
+	else
+		q->properties.doorbell_off += q->doorbell_id * 2;

This could be simplified and generalized as

	q->properties.doorbell_off += q->doorbell_id * dev->kfd->device_info.doorbell_size / 4;

Agree, we can do this simplification.

- Shashank

Regards,
  Felix


+
  	return 0;
  }



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