[Mesa-dev] [PATCH v5 03/12] gallium: add common pipe_screen reference counting functions

[Rob Herring]

On Wed, Aug 9, 2017 at 2:18 PM, Marek Olšák <maraeo at gmail.com> wrote:
> Hi Rob,
>
> This is not enough to do screen reference counting. There are primary
> FDs and render node FDs, and we want to have only one pipe_screen for
> all kinds of FDs pointing to the same device.
>
> Imagine someone creates a pipe_screen with a render node FD, and then
> creates another pipe_screen with a primary FD. We want to return the
> same pipe_screen instance in both cases.
>
> The pipe_screen should use the render node FD for everything if it was
> created first with that FD. However, it also needs to keep the primary
> FD in order to be able to do GEM_FLINK when required.
>
> libdrm_amdgpu handles all those cases correctly. It has "fd", which is
> the main one, but also has "flink_fd" for GEM_FLINK. If "fd" is a
> primary FD or there is no primary FD, "fd == flink_fd". If "fd" is a
> render node and a primary FD has also been used to create the device
> object, "fd" is the render node and "flink_fd" is the primary FD for
> GEM_FLINK.
>
> The code:
> https://cgit.freedesktop.org/mesa/drm/tree/amdgpu/amdgpu_device.c
>
> I can't accept this patch, because it effectively disables that
> amdgpu_device code.

This patch alone doesn't change any driver. I think you mean patch #8
which converts amdgpu and which could be dropped (though I'd like to
keep the radeon winsys parts). However, I believe I've maintained the
behavior for amdgpu.

The amdgpu winsys does not use the fd in these functions (the screen
fd will be -1). The only change should be that the mutex is removed
and the pipe_reference is moved from ws->reference to
ws->base.screen->reference. It's still using the device in the hash
table.

Rob