[PATCH] drm/mediatek: stop iterating dma addresses when sg_dma_len() == 0

[Chun-Kuang Hu]

Hi, Anand:

Anand Mistry <amistry at chromium.org> 於 2020年5月7日 週四 下午7:56寫道：
>
> On Wed, May 6, 2020 at 10:59 PM Chun-Kuang Hu <chunkuang.hu at kernel.org> wrote:
> >
> > Hi, Anand:
> >
> > Anand Mistry <amistry at chromium.org> 於 2020年5月6日 週三 下午7:03寫道：
> > >
> > > On Wed, May 6, 2020 at 10:25 AM Chun-Kuang Hu <chunkuang.hu at kernel.org> wrote:
> > > >
> > > > Hi, Anand,
> > > >
> > > > Chun-Kuang Hu <chunkuang.hu at kernel.org> 於 2020年4月29日 週三 上午12:37寫道：
> > > > >
> > > > > Hi, Anand,
> > > > >
> > > > > Anand K. Mistry <amistry at chromium.org> 於 2020年4月28日 週二 上午9:54寫道：
> > > > > >
> > > > > > On Sun, 26 Apr 2020 at 18:04, Chun-Kuang Hu <chunkuang.hu at kernel.org> wrote:
> > > > > > >
> > > > > > > Hi, Anand:
> > > > > > >
> > > > > > > Anand K Mistry <amistry at chromium.org> 於 2020年4月20日 週一 下午2:09寫道：
> > > > > > > >
> > > > > > > > If dma_map_sg() merges pages when creating the mapping, only the first
> > > > > > > > entries will have a valid sg_dma_address() and sg_dma_len(), followed by
> > > > > > > > entries with sg_dma_len() == 0.
> > > > > > > >
> > > > > > > > Signed-off-by: Anand K Mistry <amistry at google.com>
> > > >
> > > > Author should sign off this patch, please give a sign off tag by author.
> > >
> > > Sorry, email issues meant i sent the patch from a different account.
> > > Should I re-send the
> > > patch from the same account as the sign-off line? I'm still working my
> > > way through the kernel patch process.
> > >
> >
> > If you want to use chromium account, you could simply reply this email
> > with a sign-off-by tag of chromium account.
>
> Ack. As path of least resistance, here:
>
> Signed-off-by: Anand K Mistry <amistry at chromium.org>
>

Applied to mediatek-drm-next [1], thanks.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/chunkuang.hu/linux.git/log/?h=mediatek-drm-next

Regards,
Chun-Kuang.

>
> >
> > Regards,
> > Chun-Kuang.
> >
> > > >
> > > > Regards,
> > > > Chun-Kuang.
> > > >
> > > > > > > > ---
> > > > > > > >  drivers/gpu/drm/mediatek/mtk_drm_gem.c | 3 +++
> > > > > > > >  1 file changed, 3 insertions(+)
> > > > > > > >
> > > > > > > > diff --git a/drivers/gpu/drm/mediatek/mtk_drm_gem.c b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> > > > > > > > index b04a3c2b111e09..f8fd8b98c30e3d 100644
> > > > > > > > --- a/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> > > > > > > > +++ b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> > > > > > > > @@ -224,6 +224,9 @@ struct drm_gem_object *mtk_gem_prime_import_sg_table(struct drm_device *dev,
> > > > > > > >
> > > > > > > >         expected = sg_dma_address(sg->sgl);
> > > > > > > >         for_each_sg(sg->sgl, s, sg->nents, i) {
> > > > > > > > +               if (!sg_dma_len(s))
> > > > > > > > +                       break;
> > > > > > >
> > > > > > > I think this should be 'continue'
> > > > > >
> > > > > > scatterlist.h has the comment:
> > > > > > /*
> > > > > >  * These macros should be used after a dma_map_sg call has been done
> > > > > >  * to get bus addresses of each of the SG entries and their lengths.
> > > > > >  * You should only work with the number of sg entries dma_map_sg
> > > > > >  * returns, or alternatively stop on the first sg_dma_len(sg) which
> > > > > >  * is 0.
> > > > > >  */
> > > > > >
> > > > > > So breaking on the first sg_dma_len(sg) == 0 appears to be (one of)
> > > > > > the documented approach.
> > > > > >
> > > > >
> > > > > Okay, you're right. So
> > > > >
> > > > > Reviewed-by: Chun-Kuang Hu <chunkuang.hu at kernel.org>
> > > > >
> > > > > > >
> > > > > > > Regards,
> > > > > > > Chun-Kuang.
> > > > > > >
> > > > > > > > +
> > > > > > > >                 if (sg_dma_address(s) != expected) {
> > > > > > > >                         DRM_ERROR("sg_table is not contiguous");
> > > > > > > >                         ret = -EINVAL;
> > > > > > > > --
> > > > > > > > 2.26.1.301.g55bc3eb7cb9-goog
> > > > > > > >
> > > > > > > >
> > > > > > > > _______________________________________________
> > > > > > > > Linux-mediatek mailing list
> > > > > > > > Linux-mediatek at lists.infradead.org
> > > > > > > > http://lists.infradead.org/mailman/listinfo/linux-mediatek