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

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Date:   Wed, 15 Nov 2017 15:24:41 +0100
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Liviu Dudau <Liviu.Dudau@....com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     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


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.

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
>>