linux-kernel - Re: [PATCH] dma-buf: refcount the attachment for cache_sgt

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Date:   Wed, 12 Jun 2019 08:20:41 +0000
From:   "Koenig, Christian" <Christian.Koenig@....com>
To:     Nicolin Chen <nicoleotsuka@...il.com>
CC:     "sumit.semwal@...aro.org" <sumit.semwal@...aro.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "daniel.vetter@...ll.ch" <daniel.vetter@...ll.ch>
Subject: Re: [PATCH] dma-buf: refcount the attachment for cache_sgt_mapping

Am 12.06.19 um 10:15 schrieb Nicolin Chen:
> Hi Christian,
>
> On Wed, Jun 12, 2019 at 08:05:53AM +0000, Koenig, Christian wrote:
>> Am 12.06.19 um 10:02 schrieb Nicolin Chen:
>> [SNIP]
>>> We haven't used DRM/GRM_PRIME yet but I am also curious would it
>>> benefit DRM also if we reduce this overhead in the dma_buf?
>> No, not at all.
>  From you replies, in a summary, does it means that there won't be a case
> of DRM having a dma_buf attaching to the same device, i.e. multiple calls
> of drm_gem_prime_import() function with same parameters of dev + dma_buf?

Well, there are some cases where this happens. But in those cases we 
intentionally want to get a new attachment :)

So thinking more about it you would actually break those and that is not 
something we can do.

> If so, we can just ignore/drop this patch. Sorry for the misunderstanding.

It might be interesting for things like P2P, but even then it might be 
better to just cache the P2P settings instead of the full attachment.

Regards,
Christian.

>
> Thanks
> Nicolin