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

From: Anand Mistry <amistry@chromium.org>
To: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Cc: Anand K Mistry <amistry@google.com>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	CK Hu <ck.hu@mediatek.com>,
	"moderated list:ARM/Mediatek SoC support"
	<linux-mediatek@lists.infradead.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] drm/mediatek: stop iterating dma addresses when sg_dma_len() == 0
Date: Wed, 6 May 2020 21:03:36 +1000	[thread overview]
Message-ID: <CAECpkiM5ez8=iEe=fYKiDf5Pb6AHrTyt5uXqJQtQpQJHotupWA@mail.gmail.com> (raw)
In-Reply-To: <CAAOTY_9+s8EknSFLyYHNDfJuxERTuubBXaQ41Y3J+DeuDMFGqA@mail.gmail.com>

On Wed, May 6, 2020 at 10:25 AM Chun-Kuang Hu <chunkuang.hu@kernel.org> wrote:
>
> Hi, Anand,
>
> Chun-Kuang Hu <chunkuang.hu@kernel.org> 於 2020年4月29日 週三 上午12:37寫道：
> >
> > Hi, Anand,
> >
> > Anand K. Mistry <amistry@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@kernel.org> wrote:
> > > >
> > > > Hi, Anand:
> > > >
> > > > Anand K Mistry <amistry@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@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.

>
> 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@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@lists.infradead.org
> > > > > http://lists.infradead.org/mailman/listinfo/linux-mediatek

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