linux-kernel - Re: [RFC][PATCH 2/2] dma-buf: heaps: Fix the name used when exporting dmabufs to be the actual heap name

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Date:   Mon, 8 Feb 2021 11:08:44 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Chris Goldsworthy <cgoldswo@...eaurora.org>,
        Laura Abbott <labbott@...nel.org>,
        Brian Starkey <Brian.Starkey@....com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Daniel Mentz <danielmentz@...gle.com>,
        Ørjan Eide <orjan.eide@....com>,
        Robin Murphy <robin.murphy@....com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Simon Ser <contact@...rsion.fr>,
        James Jones <jajones@...dia.com>, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [RFC][PATCH 2/2] dma-buf: heaps: Fix the name used when
 exporting dmabufs to be the actual heap name

On Sat, Feb 06, 2021 at 05:47:48AM +0000, John Stultz wrote:
> By default dma_buf_export() sets the exporter name to be
> KBUILD_MODNAME. Unfortunately this may not be identical to the
> string used as the heap name (ie: "system" vs "system_heap").
> 
> This can cause some minor confusion with tooling, and there is
> the future potential where multiple heap types may be exported
> by the same module (but would all have the same name).
> 
> So to avoid all this, set the exporter exp_name to the heap name.
> 
> Cc: Daniel Vetter <daniel@...ll.ch>
> Cc: Sumit Semwal <sumit.semwal@...aro.org>
> Cc: Liam Mark <lmark@...eaurora.org>
> Cc: Chris Goldsworthy <cgoldswo@...eaurora.org>
> Cc: Laura Abbott <labbott@...nel.org>
> Cc: Brian Starkey <Brian.Starkey@....com>
> Cc: Hridya Valsaraju <hridya@...gle.com>
> Cc: Suren Baghdasaryan <surenb@...gle.com>
> Cc: Sandeep Patil <sspatil@...gle.com>
> Cc: Daniel Mentz <danielmentz@...gle.com>
> Cc: Ørjan Eide <orjan.eide@....com>
> Cc: Robin Murphy <robin.murphy@....com>
> Cc: Ezequiel Garcia <ezequiel@...labora.com>
> Cc: Simon Ser <contact@...rsion.fr>
> Cc: James Jones <jajones@...dia.com>
> Cc: linux-media@...r.kernel.org
> Cc: dri-devel@...ts.freedesktop.org
> Signed-off-by: John Stultz <john.stultz@...aro.org>

Looks reasonable to me.

I guess the main worry is "does this mean heap names become uapi", in
which case I'm maybe not so sure anymore how this will tie into the
overall gpu memory accounting story.

Since for dma-buf heaps one name per buffer is perfectly fine, since
dma-buf heaps aren't very dynamic. But on discrete gpu drivers buffers
move, so baking in the assumption that "exporter name = resource usage for
this buffer" is broken.

So I'm not sure we shouldn't instead name all the dma-buf heaps as
"dma-buf heaps" to stop this :-)
-Daniel

> ---
>  drivers/dma-buf/heaps/cma_heap.c    | 1 +
>  drivers/dma-buf/heaps/system_heap.c | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
> index 364fc2f3e499..62465d61ccc7 100644
> --- a/drivers/dma-buf/heaps/cma_heap.c
> +++ b/drivers/dma-buf/heaps/cma_heap.c
> @@ -339,6 +339,7 @@ static int cma_heap_allocate(struct dma_heap *heap,
>  	buffer->pagecount = pagecount;
>  
>  	/* create the dmabuf */
> +	exp_info.exp_name = dma_heap_get_name(heap);
>  	exp_info.ops = &cma_heap_buf_ops;
>  	exp_info.size = buffer->len;
>  	exp_info.flags = fd_flags;
> diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
> index 17e0e9a68baf..2d4afc79c700 100644
> --- a/drivers/dma-buf/heaps/system_heap.c
> +++ b/drivers/dma-buf/heaps/system_heap.c
> @@ -388,6 +388,7 @@ static int system_heap_allocate(struct dma_heap *heap,
>  	}
>  
>  	/* create the dmabuf */
> +	exp_info.exp_name = dma_heap_get_name(heap);
>  	exp_info.ops = &system_heap_buf_ops;
>  	exp_info.size = buffer->len;
>  	exp_info.flags = fd_flags;
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch