linux-kernel - Re: [PATCH] dma-buf: heaps: Introduce dma_heap_add

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Date:   Tue, 28 Jul 2020 12:17:44 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
Cc:     Sumit Semwal <sumit.semwal@...aro.org>,
        "Andrew F . Davis" <afd@...com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        Brian Starkey <Brian.Starkey@....com>,
        Christian Koenig <christian.koenig@....com>,
        linux-media@...r.kernel.org,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dma-buf: heaps: Introduce dma_heap_add_cma() for
 non-default CMA heap

On Thu, Jul 16, 2020 at 6:10 PM Kunihiko Hayashi
<hayashi.kunihiko@...ionext.com> wrote:
>
> Current dma-buf heaps can handle only default CMA. This introduces
> dma_heap_add_cma() function to attach CMA heaps that belongs to a device.
>
> At first, the driver calls of_reserved_mem_device_init() to set
> memory-region property associated with reserved-memory defined as CMA
> to the device. And when the driver calls this dma_heap_add_cma(),
> the CMA will be added to dma-buf heaps.
>
> For example, prepare CMA node named "linux,cma@...00000" and
> specify the node for memory-region property. After the above calls
> in the driver, a device file "/dev/dma_heap/linux,cma@...00000"
> associated with the CMA become available as dma-buf heaps.
>
> Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
> ---
>  drivers/dma-buf/heaps/cma_heap.c | 12 ++++++++++++
>  include/linux/dma-heap.h         |  9 +++++++++
>  2 files changed, 21 insertions(+)

Hey! Sorry for the slow response on this! I just realized I never replied!

> diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
> index 626cf7f..5d2442e 100644
> --- a/drivers/dma-buf/heaps/cma_heap.c
> +++ b/drivers/dma-buf/heaps/cma_heap.c
> @@ -162,6 +162,18 @@ static int __add_cma_heap(struct cma *cma, void *data)
>         return 0;
>  }
>
> +/* add device CMA heap to dmabuf heaps */
> +int dma_heap_add_cma(struct device *dev)
> +{
> +       struct cma *cma = dev_get_cma_area(dev);
> +
> +       if (!cma)
> +               return -ENOMEM;
> +
> +       return __add_cma_heap(cma, NULL);
> +}
> +EXPORT_SYMBOL_GPL(dma_heap_add_cma);
> +
>  static int add_default_cma_heap(void)
>  {
>         struct cma *default_cma = dev_get_cma_area(NULL);
> diff --git a/include/linux/dma-heap.h b/include/linux/dma-heap.h
> index 454e354..16bec7d 100644
> --- a/include/linux/dma-heap.h
> +++ b/include/linux/dma-heap.h
> @@ -56,4 +56,13 @@ void *dma_heap_get_drvdata(struct dma_heap *heap);
>   */
>  struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info);
>
> +#ifdef CONFIG_DMABUF_HEAPS_CMA
> +/**
> + * dma_heap_add_cma - adds a device CMA heap to dmabuf heaps
> + * @dev:       device with a CMA heap to register
> + */
> +int dma_heap_add_cma(struct device *dev);
> +
> +#endif /* CONFIG_DMABUF_HEAPS_CMA */
> +
>  #endif /* _DMA_HEAPS_H */
> --
> 2.7.4

Looks sane to me.  Being able to expose different multiple CMA heaps
is needed, and I agree this way (as opposed to my earlier dts
appraoch) is probably the best approach. The only bit I'm so-so on is
adding the CMA heap specific call in the dma-heap.h, but at the same
time I can't justify adding a whole new header for a single function.

Do you have a upstream driver that you plan to make use this new call?
We want to have in-tree users of code added.

But if so, feel free to add my:
  Acked-by: John Stultz <john.stultz@...aro.org>
To this patch when you submit the driver changes.

thanks
-john