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

quoted

@@ -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