GBM as standalone buffer allocator

[Yiwei Zhang]

There’s
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26038. It is
quite appealing to me considering a VK only scenario.

On Thu, Nov 2, 2023 at 5:50 AM Srinivas Pullakavi (QUIC) <
quic_spullaka at quicinc.com> wrote:

> Hi Rob,
>
> Thanks for your inputs.
>
> We are planning to use DMA-Buf for GBM backend. DMA-buf supported heaps
> are listed in /dev/dma_heap/
> Gbm backend selects the best heap based on usage. For example: Secure
> buffers will be allocated from secure heap.
>
> Sample output:
>                      # ls /dev/dma_heap
>                  reserved  system
>
> Sample code to allocate a buffer from system heap:
>         int heap_fd = open(/dev/dma_heap/system, O_RDONLY | O_CLOEXEC))
>         struct dma_heap_allocation_data heap_data {
>               .len = size,                      // length of data to be
> allocated in bytes
>               .fd_flags = O_RDWR | O_CLOEXEC,   // permissions for the
> memory to be allocated
>               };
>         int status = ioctl(heap_fd, DMA_HEAP_IOCTL_ALLOC, &heap_data)
>         if (status == 0) {
>                  int buffer_fd = heap_data.fd;
>               }
>
> In this case, there is no dependency on display / Graphics driver. But
> still GBM create device expects a device fd to be passed.
>
> Can we make it optional to pass device fd ?
>
> Thanks,
> Srinivas
>
> -----Original Message-----
> From: Rob Clark <robdclark at gmail.com>
> Sent: Tuesday, October 24, 2023 1:06 AM
> To: Srinivas Pullakavi (QUIC) <quic_spullaka at quicinc.com>
> Cc: mesa-dev at lists.freedesktop.org
> Subject: Re: GBM as standalone buffer allocator
>
> On Mon, Oct 23, 2023 at 6:22 AM Srinivas Pullakavi (QUIC) <
> quic_spullaka at quicinc.com> wrote:
> >
> > Hi,
> >
> >
> >
> > We are planning to enhance GBM as a standalone buffer allocator, which
> > can be used for all multi-media clients. Ex: video, camera, display
> > etc;
> >
> >
> >
> > GBM create device expects a file descriptor to be passed, which points
> to drm node. This brings in a dependency on display for buffer allocation.
> On headless devices where display driver is not present, GBM cannot be used
> for buffer allocations. E.g. Recording cases where pipeline is setup
> between Camera, Video, Graphics.
> >
>
> Note that you need some sort of device to allocate buffers from.  With
> mesa and upstream kernel, that would be the drm device.  (However as Adam
> points out, a drm device does not necessarily need a display..
> for example, several vendors have compute-only GPUs (pci) which have no
> display outputs.)
>
> You might want to look at ChromeOS's minigbm.  It already handles these
> cases (buffer sharing across display/gpu/video/camera).
>
> BR,
> -R
>
> [1] https://chromium.googlesource.com/chromiumos/platform/minigbm/
>
> >
> > Could you please share your comments on what will be a good design to
> make GBM flexible for above?
> >
> >
> >
> > Thanks,
> >
> > Srinivas
> >
> >
>
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