Am 2021-08-15 um 5:10 a.m. schrieb Christoph Hellwig:

...

@@ -880,17 +881,22 @@ int svm_migrate_init(struct amdgpu_device *adev) * should remove reserved size */ size = ALIGN(adev->gmc.real_vram_size, 2ULL << 20);

• res = devm_request_free_mem_region(adev->dev, &iomem_resource, size);

• if (xgmi_connected_to_cpu)

• res = lookup_resource(&iomem_resource, adev->gmc.aper_base);
  

• else

• res = devm_request_free_mem_region(adev->dev, &iomem_resource, size);
  

Can you explain what the point of the lookup_resource is here? res->start is obviously identical to the start value you pass in. So this is used as a way to query the length, but I'm pretty sure the driver must already know that as it inserted the resource itself, right?

I think you're right. We only need the start and end address from lookup_resource and we already know that anyway. It means we can drop patch 3 from the series.

Just to be sure, we'll confirm that the end address determined by our driver matches the one from lookup_resource (coming from the system address map in the system BIOS). If there were a mismatch, it would probably be a bug (in the driver or the BIOS) that we'd need to fix anyway.

On a slightly higher level comment svm_migrate_init is a bit of a mess with all the if/else already, and with the above addressed will become a bit more. I think splitting it into a device private and device generic case would probably help people finding it to understand the code much better later on. Even more so with a useful comment.

I don't really see the "mess" you're talking about. Including the above, there are only 3 conditional statements in that function that are not error-handling related:

/* Page migration works on Vega10 or newer */ if (kfddev->device_info->asic_family < CHIP_VEGA10) return -EINVAL; ... if (xgmi_connected_to_cpu) res = lookup_resource(&iomem_resource, adev->gmc.aper_base); else res = devm_request_free_mem_region(adev->dev, &iomem_resource, size); ... pgmap->type = xgmi_connected_to_cpu ? MEMORY_DEVICE_GENERIC : MEMORY_DEVICE_PRIVATE;

Regards,   Felix