Re: [PATCH] drm/i915: Before pageflip, also wait for shared dmabuf fences.

On Wed, Sep 21, 2016 at 06:23:35PM +0200, Christian König wrote:

For a quick workaround I suggest to just serialize all accesses to BO shared with different drivers, but essentially I think it is a perfectly valid requirement to have multiple writers to one BO.

It is, but it's not possible with implicit sync. If you want parallel write access to the same shared buffer, you _must_ carry around some explicit fences. Within amdgpu you can use driver-specific cookies, for shared buffer we now have sync_file. But multiple writers with implicit sync simply fundamentally doesn't work. Because you have no idea with which writer, touching the same subrange you want to touch. -Daniel