From: Vivek Gautam <vivek.gautam@codeaurora.org>
To: Rob Clark <robdclark@gmail.com>
Cc: hch@infradead.org, David Airlie <airlied@linux.ie>,
Tomasz Figa <tfiga@chromium.org>,
open list <linux-kernel@vger.kernel.org>,
freedreno <freedreno@lists.freedesktop.org>,
dri-devel <dri-devel@lists.freedesktop.org>,
linux-arm-msm <linux-arm-msm@vger.kernel.org>,
Jordan Crouse <jcrouse@codeaurora.org>,
Sean Paul <seanpaul@chromium.org>
Subject: Re: [PATCH v2 1/1] drm: msm: Replace dma_map_sg with dma_sync_sg*
Date: Thu, 29 Nov 2018 15:14:21 +0530 [thread overview]
Message-ID: <CAFp+6iFDanGLoWf95CR2Etq76tC8+dpciOcJzou4QfAUO3WRQA@mail.gmail.com> (raw)
In-Reply-To: <CAF6AEGuM-R0=KRSmT+bt6SBaZg_ea3A_YFE+xfR_oCH9d9uORA@mail.gmail.com>
On Wed, Nov 28, 2018 at 6:09 PM Rob Clark <robdclark@gmail.com> wrote:
>
> On Wed, Nov 28, 2018 at 2:39 AM Christoph Hellwig <hch@infradead.org> wrote:
> >
> > > + /*
> > > + * dma_sync_sg_*() flush the physical pages, so point
> > > + * sg->dma_address to the physical ones for the right behavior.
> > > + */
> > > + for_each_sg(msm_obj->sgt->sgl, s, msm_obj->sgt->nents, i)
> > > + sg_dma_address(s) = sg_phys(s);
> > > +
> >
> > I'm sorry, but this is completely bogus and not acceptable.
> >
> > The only place that is allowed to initialize sg_dma_address is
> > dma_map_sg. If the default dma ops don't work for your setup we have
> > major a problem and need to fix the dma api / iommu integration instead
> > of hacking around it.
>
> I agree that the dma/iommu integration is very problematic for drm (in
> particular, gpu drivers that use the iommu as an gpu mmu).. Really we
> need a way that a driver can opt-out of this, and access the cpu cache
> APIs directly, skipping the dma API entirely. But as it is, we've had
> to hack around the dma API. I'm not really sure this hack is any
> worse than abusing dma_(un)map_sg() for doing cache operations.
>
> I probably should have paid more attention and nak'd the dma/iommu
> integration before it landed. But given that now we are stuck in this
> situation, while I'm certainly interested if anyone has some ideas
> about how to let drivers opt out of the dma/iommu integration and
> bypass the dma API layer, I'm ok with replacing a hack with a less-bad
> hack.
May I take it as a positive nod to respin the next version?
Regards
Vivek
>
> BR,
> -R
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation
next prev parent reply other threads:[~2018-11-29 9:44 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-26 21:37 [PATCH v2 1/1] drm: msm: Replace dma_map_sg with dma_sync_sg* Vivek Gautam
2018-11-28 3:09 ` Tomasz Figa
2018-11-29 9:43 ` Vivek Gautam
2018-11-28 7:39 ` Christoph Hellwig
2018-11-28 9:02 ` Vivek Gautam
2018-11-28 12:38 ` Rob Clark
2018-11-29 9:44 ` Vivek Gautam [this message]
2018-11-28 14:19 ` Lukas Wunner
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