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 <[email protected]>
Sent: Tuesday, October 24, 2023 1:06 AM
To: Srinivas Pullakavi (QUIC) <[email protected]>
Cc: [email protected]
Subject: Re: GBM as standalone buffer allocator
On Mon, Oct 23, 2023 at 6:22 AM Srinivas Pullakavi (QUIC)
<[email protected]> 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
>
>
