Hi Brian, Thanks a lot for reviewing this patch. I'm happy my humble proof-of-concept is able to spark some interest and raise some questions. On Mon, 2020-08-17 at 16:18 +0100, Brian Starkey wrote: > Hi Ezequiel, > > On Sun, Aug 16, 2020 at 02:22:46PM -0300, Ezequiel Garcia wrote: > > This heap is basically a wrapper around DMA-API dma_alloc_attrs, > > which will allocate memory suitable for the given device. > > > > The implementation is mostly a port of the Contiguous Videobuf2 > > memory allocator (see videobuf2/videobuf2-dma-contig.c) > > over to the DMA-BUF Heap interface. > > > > The intention of this allocator is to provide applications > > with a more system-agnostic API: the only thing the application > > needs to know is which device to get the buffer for. > > > > Whether the buffer is backed by CMA, IOMMU or a DMA Pool > > is unknown to the application. > > > > I'm not really expecting this patch to be correct or even > > a good idea, but just submitting it to start a discussion on DMA-BUF > > heap discovery and negotiation. > > > > My initial reaction is that I thought dmabuf heaps are meant for use > to allocate buffers for sharing across devices, which doesn't fit very > well with having per-device heaps. > That's true. > For single-device allocations, would using the buffer allocation > functionality of that device's native API be better in most > cases? (Some other possibly relevant discussion at [1]) > That may be true for existing subsystems. However, how about a new subsystem/API wanting to leverage the heap API and avoid exposing yet another allocator API? And then, also, if we have an allocator API, perhaps we could imagine a future where applications would only need to worry about that, and not about each per-framework allocator. > I can see that this can save some boilerplate for devices that want > to expose private chunks of memory, but might it also lead to 100 > aliases for the system's generic coherent memory pool? > The idea (even if PoC) was to let drivers decide if they are special enough to add themselves (via dev_dma_heap_add). Aliasing the heap would be ceratainly too much (although trying it for every device was a fun experiment to watch). Thanks, Ezequiel > I wonder if a set of helpers to allow devices to expose whatever they > want with minimal effort would be better. > > Cheers, > -Brian > > 1. https://lore.kernel.org/dri-devel/57062477-30e7-a3de-6723-a50d03a402c4@xxxxxxxx/ > > > Given Plumbers is just a couple weeks from now, I've submitted > > a BoF proposal to discuss this, as perhaps it would make > > sense to discuss this live? > > > > Not-signed-off-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
