From: Daniel Vetter <daniel@ffwll.ch>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>,
Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
DRI Development <dri-devel@lists.freedesktop.org>,
DMA BUFFER SHARING FRAMEWORK <linux-media@vger.kernel.org>
Subject: Re: [Intel-gfx] [PATCH] drm-buf: Add debug option
Date: Thu, 14 Jan 2021 10:47:40 +0100 [thread overview]
Message-ID: <YAATPMc+1jmhxnsF@phenom.ffwll.local> (raw)
In-Reply-To: <161061753732.19482.13146900597152116822@build.alporthouse.com>
On Thu, Jan 14, 2021 at 09:45:37AM +0000, Chris Wilson wrote:
> Quoting Daniel Vetter (2021-01-14 09:30:32)
> > On Thu, Jan 14, 2021 at 10:23 AM Chris Wilson <chris@chris-wilson.co.uk> wrote:
> > > The only other problem I see with the implementation is that there's
> > > nothing that says that each dmabuf->ops->map_dma_buf() returns a new
> > > sg_table, so we may end up undoing the xor. Or should each dma-buf
> > > return a fresh dma-mapping for iommu isolation?
> >
> > Maybe I screwed it up, but that's why I extracted the little helpers:
> > We scramble when we get the sgtable from exporter, and unscramble
> > before we pass it back. dma-buf.c does some caching and will hand back
> > the same sgtable, but for that case we don't re-scramble.
>
> The attachment is only mapped once, but there can be more than one
> attachment, and the backend could return the same sg_table for each
> mapping. Conceivably, it could return its own private sg_table where it
> wants to maintain the struct page. Seems like just adding a sentence to
> @map_dma_buf to clarify that each call should return a new sg_table will
> suffice.
Ah yes good point, will augment (once CI stops being angry at me).
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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next prev parent reply other threads:[~2021-01-14 9:47 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-13 14:06 [PATCH] drm-buf: Add debug option Daniel Vetter
2021-01-13 15:43 ` [Intel-gfx] " Chris Wilson
2021-01-13 20:50 ` Daniel Vetter
2021-01-13 21:08 ` Chris Wilson
2021-01-14 9:02 ` Daniel Vetter
2021-01-14 9:23 ` Chris Wilson
2021-01-14 9:30 ` Daniel Vetter
2021-01-14 9:45 ` Chris Wilson
2021-01-14 9:47 ` Daniel Vetter [this message]
2021-01-15 8:25 ` Chris Wilson
2021-01-15 20:08 ` John Stultz
2021-02-17 3:30 ` John Stultz
2021-02-17 3:34 ` John Stultz
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