linux-kernel - Re: [PATCH v2] drm: gem_cma_helper.c: Allow importing of contiguous scatterlists with nents

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Message-ID: <20171115144117.GC31361@e110455-lin.cambridge.arm.com>
Date:   Wed, 15 Nov 2017 14:41:17 +0000
From:   Liviu Dudau <Liviu.Dudau@....com>
To:     Noralf Trønnes <noralf@...nnes.org>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        intel-gfx@...ts.freedesktop.org,
        LKML <linux-kernel@...r.kernel.org>,
        DRI-devel <dri-devel@...ts.freedesktop.org>,
        Mali DP Maintainers <malidp@...s.arm.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH v2] drm: gem_cma_helper.c: Allow importing of contiguous
 scatterlists with nents > 1

On Wed, Nov 15, 2017 at 03:24:41PM +0100, Noralf Trønnes wrote:
> 
> Den 15.11.2017 14.04, skrev Liviu Dudau:
> > Hi,
> > 
> > On Sat, Nov 11, 2017 at 02:47:35PM +0200, Laurent Pinchart wrote:
> > > Hi Liviu,
> > > 
> > > Thank you for the patch.
> > > 
> > > On Friday, 10 November 2017 15:33:10 EET Liviu Dudau wrote:
> > > > drm_gem_cma_prime_import_sg_table() will fail if the number of entries
> > > > in the sg_table > 1. However, you can have a device that uses an IOMMU
> > > > engine and can map a discontiguous buffer with multiple entries that
> > > > have consecutive sg_dma_addresses, effectively making it contiguous.
> > > > Allow for that scenario by testing the entries in the sg_table for
> > > > contiguous coverage.
> > > > 
> > > > Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > > > Signed-off-by: Liviu Dudau <liviu.dudau@....com>
> > > > ---
> > > > 
> > > > Laurent,
> > > > 
> > > > Thanks for the review! I would like to ask for one more favour: if you
> > > > are OK with this version, can you pull this patch through the drm-misc tree?
> > > I could, but I'd first need to set dim up, and I'm currently abroad with a bad
> > > internet connection and a big deadline for the middle of next week (I know,
> > > lots of excuses), so it's not very convenient for me at this time.
> > Any other drm-misc maintainers feeling helpful and willing to take this
> > patch in?
> 
> Sure, I can do it this evening.

Cheers, much appreciated!

Best regards,
Liviu

> 
> Noralf.
> 
> >   Otherwise I can send it through the mali-dp tree if no one
> > objects.
> > 
> > Best regards,
> > Liviu
> > 
> > > >   drivers/gpu/drm/drm_gem_cma_helper.c | 22 ++++++++++++++++++++--
> > > >   include/drm/drm_gem_cma_helper.h     |  4 +++-
> > > >   2 files changed, 23 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c
> > > > b/drivers/gpu/drm/drm_gem_cma_helper.c index 020e7668dfaba..43b179212052d
> > > > 100644
> > > > --- a/drivers/gpu/drm/drm_gem_cma_helper.c
> > > > +++ b/drivers/gpu/drm/drm_gem_cma_helper.c
> > > > @@ -482,8 +482,26 @@ drm_gem_cma_prime_import_sg_table(struct drm_device
> > > > *dev, {
> > > >   	struct drm_gem_cma_object *cma_obj;
> > > > 
> > > > -	if (sgt->nents != 1)
> > > > -		return ERR_PTR(-EINVAL);
> > > > +	if (sgt->nents != 1) {
> > > > +		/* check if the entries in the sg_table are contiguous */
> > > > +		dma_addr_t next_addr = sg_dma_address(sgt->sgl);
> > > > +		struct scatterlist *s;
> > > > +		unsigned int i;
> > > > +
> > > > +		for_each_sg(sgt->sgl, s, sgt->nents, i) {
> > > > +			/*
> > > > +			 * sg_dma_address(s) is only valid for entries
> > > > +			 * that have sg_dma_len(s) != 0
> > > > +			 */
> > > > +			if (!sg_dma_len(s))
> > > > +				continue;
> > > > +
> > > > +			if (sg_dma_address(s) != next_addr)
> > > > +				return ERR_PTR(-EINVAL);
> > > > +
> > > > +			next_addr = sg_dma_address(s) + sg_dma_len(s);
> > > > +		}
> > > > +	}
> > > > 
> > > >   	/* Create a CMA GEM buffer. */
> > > >   	cma_obj = __drm_gem_cma_create(dev, attach->dmabuf->size);
> > > > diff --git a/include/drm/drm_gem_cma_helper.h
> > > > b/include/drm/drm_gem_cma_helper.h index 58a739bf15f1f..214aa85adc8d5
> > > > 100644
> > > > --- a/include/drm/drm_gem_cma_helper.h
> > > > +++ b/include/drm/drm_gem_cma_helper.h
> > > > @@ -8,7 +8,9 @@
> > > >    * struct drm_gem_cma_object - GEM object backed by CMA memory allocations
> > > >    * @base: base GEM object
> > > >    * @paddr: physical address of the backing memory
> > > > - * @sgt: scatter/gather table for imported PRIME buffers
> > > > + * @sgt: scatter/gather table for imported PRIME buffers. The table can
> > > > have + *       more than one entry but they are guaranteed to have
> > > > contiguous + *       DMA addresses.
> > > >    * @vaddr: kernel virtual address of the backing memory
> > > >    */
> > > >   struct drm_gem_cma_object {
> > > -- 
> > > Regards,
> > > 
> > > Laurent Pinchart
> > > 
> 

-- 
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