[PATCH weston] compositor-drm: disable hardware cursors

[Pekka Paalanen]

On Tue, 19 May 2015 10:26:10 +0300
Pekka Paalanen <ppaalanen at gmail.com> wrote:

> From: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
> 
> With the recent universal plane and atomic modeset / nuclear pageflip
> development in the kernel, cursor content updates on Intel are currently causing
> an extra wait for vblank. This drops Weston's framerate to a fraction by
> 2 when cursor contents update. This combined with the damage tracking
> bug in Weston which causes cursor content updates on every frame the
> cursor moves makes using hw cursors really bad.
> 
> It is possible that the Intel DRM driver will get fixed and cursor
> updates there revert to their old behaviour on the contemporary KMS API.
> However, it is hardware dependant whether cursor updates can happen
> immediately.  Some other hardware, especially ARM-related, may not be
> able to do immediate updates. Therefore it is better to just not even
> try - we should rely only on the lowest common denominator behaviour
> between hardware and drivers as there is no and will not be any way to
> reliably detect it.
> 
> Note, that while having different drivers do different things (immediate
> update vs. update that gets latched on the next vblank), we cannot
> rearrange the contemporary KMS API calls such that it would always work
> fine. Either some hardware would update the cursor too early, or other
> hardware would update the cursor too late and perhaps cause the
> framerate decimation.
> 
> Mark hardware cursors broken by default. This avoids using them, and
> works around the immediate problem of framerate issues in Weston. This
> follows the same reasoning why hardware overlay planes have been
> disabled by default for a long time.
> 
> This disablement will be removed once the current code for hardware
> planes and cursors is replaced with code using the atomic KMS API.
> 
> The Intel driver change that exposed this problem is
> https://github.com/torvalds/linux/commit/38f3ce3af5742eb5a3e9b01997f5ab85109c5762
> which is first included in Linux 4.0-rc1.
> 
> Signed-off-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
> Cc: nerdopolis <bluescreen_avenger at verizon.net>
> Cc: Daniel Stone <daniel at fooishbar.org>
> Cc: Giulio Camuffo <giuliocamuffo at gmail.com>
> ---

With Daniel's (irc) and David's R-bs, pushed.
   c4cfe85..6858383  master -> master


Thanks,
pq