Re: [PATCH 1/2] drm: allow limiting the scatter list size.

[Christian König]

Am 18.08.20 um 10:27 schrieb Gerd Hoffmann:
> On Tue, Aug 18, 2020 at 09:57:59AM +0200, Christian König wrote:
> > Am 18.08.20 um 09:48 schrieb Gerd Hoffmann:
> > > Add max_segment argument to drm_prime_pages_to_sg().  When set pass it
> > > through to the __sg_alloc_table_from_pages() call, otherwise use
> > > SCATTERLIST_MAX_SEGMENT.
> > >
> > > Also add max_segment field to gem objects and pass it to
> > > drm_prime_pages_to_sg() calls in drivers and helpers.
> > >
> > > Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> > I'm missing an explanation why this should be useful (it certainly is).
> virtio-gpu needs this to work properly with SEV (see patch 2/2 of this
> series).

Yeah, that's the problem patch 2/2 never showed up here :)

> > And the maximum segment size seems misplaced in the GEM object. This is
> > usually a property of the device or even completely constant.
> Placing it in drm_device instead would indeed work for virtio-gpu, so I
> guess you are suggesting that instead?

That is probably the best approach, yes.

For Intel and AMD it could even be global/constant, but it certainly 
doesn't needs to be kept around for each buffer.

Christian.

> take care,
>    Gerd