Re: [PATCH] drm: don't block fb changes for async plane updates

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Jun 10, 2019 at 10:36:27AM -0300, Helen Koike wrote:
> commit 89a4aac0ab0e6f5eea10d7bf4869dd15c3de2cd4 upstream.
> 
> In the case of a normal sync update, the preparation of framebuffers (be
> it calling drm_atomic_helper_prepare_planes() or doing setups with
> drm_framebuffer_get()) are performed in the new_state and the respective
> cleanups are performed in the old_state.
> 
> In the case of async updates, the preparation is also done in the
> new_state but the cleanups are done in the new_state (because updates
> are performed in place, i.e. in the current state).
> 
> The current code blocks async udpates when the fb is changed, turning
> async updates into sync updates, slowing down cursor updates and
> introducing regressions in igt tests with errors of type:
> 
> "CRITICAL: completed 97 cursor updated in a period of 30 flips, we
> expect to complete approximately 15360 updates, with the threshold set
> at 7680"
> 
> Fb changes in async updates were prevented to avoid the following scenario:
> 
> - Async update, oldfb = NULL, newfb = fb1, prepare fb1, cleanup fb1
> - Async update, oldfb = fb1, newfb = fb2, prepare fb2, cleanup fb2
> - Non-async commit, oldfb = fb2, newfb = fb1, prepare fb1, cleanup fb2 (wrong)
> Where we have a single call to prepare fb2 but double cleanup call to fb2.
> 
> To solve the above problems, instead of blocking async fb changes, we
> place the old framebuffer in the new_state object, so when the code
> performs cleanups in the new_state it will cleanup the old_fb and we
> will have the following scenario instead:
> 
> - Async update, oldfb = NULL, newfb = fb1, prepare fb1, no cleanup
> - Async update, oldfb = fb1, newfb = fb2, prepare fb2, cleanup fb1
> - Non-async commit, oldfb = fb2, newfb = fb1, prepare fb1, cleanup fb2
> 
> Where calls to prepare/cleanup are balanced.
> 
> Cc: <stable@vger.kernel.org> # v4.14+
> Fixes: 25dc194b34dd ("drm: Block fb changes for async plane updates")
> Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
> Signed-off-by: Helen Koike <helen.koike@collabora.com>
> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
> Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> Link: https://patchwork.freedesktop.org/patch/msgid/20190603165610.24614-6-helen.koike@collabora.com
> ---
> 
> Hi,
> 
> This patch failed to apply on kernel stable v4.14, I'm re-sending it
> fixing the conflict.

Now applied, thanks.

greg k-h