Re: [PATCH v5 05/38] drm: prime: use sgtable iterators in drm_prime_sg_to_page_addr_arrays()

From: Marek Szyprowski
Date: Tue Sep 22 2020 - 02:28:08 EST

Hi Alex,

On 22.09.2020 01:15, Alex Goins wrote:
> Tested-by: Alex Goins <agoins@xxxxxxxxxx>
> This change fixes a regression with drm_prime_sg_to_page_addr_arrays() and
> AMDGPU in v5.9.

Thanks for testing!

> Commit 39913934 similarly revamped AMDGPU to use sgtable helper functions. When
> it changed from dma_map_sg_attrs() to dma_map_sgtable(), as a side effect it
> started correctly updating sgt->nents to the return value of dma_map_sg_attrs().
> However, drm_prime_sg_to_page_addr_arrays() incorrectly uses sgt->nents to
> iterate over pages, rather than sgt->orig_nents, resulting in it now returning
> the incorrect number of pages on AMDGPU.
> I had written a patch that changes drm_prime_sg_to_page_addr_arrays() to use
> for_each_sgtable_sg() instead of for_each_sg(), iterating using sgt->orig_nents:
> - for_each_sg(sgt->sgl, sg, sgt->nents, count) {
> + for_each_sgtable_sg(sgt, sg, count) {
> This patch takes it further, but still has the effect of fixing the number of
> pages that drm_prime_sg_to_page_addr_arrays() returns. Something like this
> should be included in v5.9 to prevent a regression with AMDGPU.

Probably the easiest way to handle a fix for v5.9 would be to simply
merge the latest version of this patch also to v5.9-rcX:

This way we would get it fixed and avoid possible conflict in the -next.
Do you have any AMDGPU fixes for v5.9 in the queue? Maybe you can add
that patch to the queue? Dave: would it be okay that way?

Best regards
Marek Szyprowski, PhD
Samsung R&D Institute Poland