Re: [RFC][PATCH 3/4] dma-buf: cma_heap: Extend logic to export CMA regions tagged with "linux,cma-heap"

[Robin Murphy]

On 2020-05-01 11:21 am, Brian Starkey wrote:
> Hi John,
>
> On Fri, May 01, 2020 at 07:39:48AM +0000, John Stultz wrote:
> > This patch reworks the cma_heap initialization so that
> > we expose both the default CMA region and any CMA regions
> > tagged with "linux,cma-heap" in the device-tree.
> >
> > Cc: Rob Herring <robh+dt@xxxxxxxxxx>
> > Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
> > Cc: "Andrew F. Davis" <afd@xxxxxx>
> > Cc: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxx>
> > Cc: Liam Mark <lmark@xxxxxxxxxxxxxx>
> > Cc: Pratik Patel <pratikp@xxxxxxxxxxxxxx>
> > Cc: Laura Abbott <labbott@xxxxxxxxxx>
> > Cc: Brian Starkey <Brian.Starkey@xxxxxxx>
> > Cc: Chenbo Feng <fengc@xxxxxxxxxx>
> > Cc: Alistair Strachan <astrachan@xxxxxxxxxx>
> > Cc: Sandeep Patil <sspatil@xxxxxxxxxx>
> > Cc: Hridya Valsaraju <hridya@xxxxxxxxxx>
> > Cc: Christoph Hellwig <hch@xxxxxx>
> > Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> > Cc: Robin Murphy <robin.murphy@xxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: devicetree@xxxxxxxxxxxxxxx
> > Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > Cc: linux-mm@xxxxxxxxx
> > Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
> > ---
> >   drivers/dma-buf/heaps/cma_heap.c | 18 +++++++++---------
> >   1 file changed, 9 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
> > index 626cf7fd033a..dd154e2db101 100644
> > --- a/drivers/dma-buf/heaps/cma_heap.c
> > +++ b/drivers/dma-buf/heaps/cma_heap.c
> > @@ -141,6 +141,11 @@ static int __add_cma_heap(struct cma *cma, void *data)
> >   {
> >   	struct cma_heap *cma_heap;
> >   	struct dma_heap_export_info exp_info;
> > +	struct cma *default_cma = dev_get_cma_area(NULL);
> > +
> > +	/* We only add the default heap and explicitly tagged heaps */
> > +	if (cma != default_cma && !cma_dma_heap_enabled(cma))
> > +		return 0;
>
> Thinking about the pl111 thread[1], I'm wondering if we should also
> let drivers call this directly to expose their CMA pools, even if they
> aren't tagged for dma-heaps in DT. But perhaps that's too close to
> policy.

That sounds much like what my first thoughts were - apologies if I'm 
wildly off-base here, but as far as I understand:

- Device drivers know whether they have their own "memory-region" or not.
- Device drivers already have to do *something* to participate in dma-buf.
- Device drivers know best how they make use of both the above.
- Therefore couldn't it be left to drivers to choose whether to register 
their CMA regions as heaps, without having to mess with DT at all?

Robin.

> Cheers,
> -Brian
>
> [1] https://lists.freedesktop.org/archives/dri-devel/2020-April/264358.html
>
> >   
> >   	cma_heap = kzalloc(sizeof(*cma_heap), GFP_KERNEL);
> >   	if (!cma_heap)
> > @@ -162,16 +167,11 @@ static int __add_cma_heap(struct cma *cma, void *data)
> >   	return 0;
> >   }
> >   
> > -static int add_default_cma_heap(void)
> > +static int cma_heaps_init(void)
> >   {
> > -	struct cma *default_cma = dev_get_cma_area(NULL);
> > -	int ret = 0;
> > -
> > -	if (default_cma)
> > -		ret = __add_cma_heap(default_cma, NULL);
> > -
> > -	return ret;
> > +	cma_for_each_area(__add_cma_heap, NULL);
> > +	return 0;
> >   }
> > -module_init(add_default_cma_heap);
> > +module_init(cma_heaps_init);
> >   MODULE_DESCRIPTION("DMA-BUF CMA Heap");
> >   MODULE_LICENSE("GPL v2");
> > --
> > 2.17.1