linux-ext4 - Re: [PATCH v6 04/13] drm/amdkfd: add SPM support for SVM

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Date:   Sun, 15 Aug 2021 11:10:00 +0200
From:   Christoph Hellwig <hch@....de>
To:     Alex Sierra <alex.sierra@....com>
Cc:     akpm@...ux-foundation.org, Felix.Kuehling@....com,
        linux-mm@...ck.org, rcampbell@...dia.com,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        hch@....de, jgg@...dia.com, jglisse@...hat.com
Subject: Re: [PATCH v6 04/13] drm/amdkfd: add SPM support for SVM

> @@ -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?

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.