[PATCH 4/4] drm/TODO: add a task to kill DRM_UNLOCKED

[Emil Velikov]

On 2019/05/22, Daniel Vetter wrote:
> On Wed, May 22, 2019 at 04:47:02PM +0100, Emil Velikov wrote:
> > From: Emil Velikov <emil.velikov at collabora.com>
> > 
> > Should minimise the copy/paste mistakes, fixed with previous patches.
> > 
> > Cc: Daniel Vetter <daniel at ffwll.ch>
> > Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
> > ---
> > Daniel, not 100% sold on the idea. That plus listing you as a contact
> > point ;-)
> > 
> > What do you thing?
> > Emil
> > ---
> >  Documentation/gpu/todo.rst | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)
> > 
> > diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
> > index 66f05f4e469f..9e67d125f2fd 100644
> > --- a/Documentation/gpu/todo.rst
> > +++ b/Documentation/gpu/todo.rst
> > @@ -397,6 +397,25 @@ Some of these date from the very introduction of KMS in 2008 ...
> >    end, for which we could add drm_*_cleanup_kfree(). And then there's the (for
> >    historical reasons) misnamed drm_primary_helper_destroy() function.
> >  
> > +Use DRM_LOCKED instead of DRM_UNLOCKED
> > +--------------------------------------
> > +
> > +DRM_UNLOCKED is a remainder from the legacy DRM drivers. Seemingly drivers get
> > +tricked by it and it ends up in the driver private ioctls.
> > +
> > +Today no more legacy drivers are allowed and most core DRM ioctls are unlocked.
> > +
> > +Introduce DRM_LOCKED, use it to annotate only the relevant ioctls and kill the
> > +old DRM_UNLOCKED.
> > +
> > +Patch series should be split as follows:
> > + - Patch 1: drm: add the new DRM_LOCKED flag and honour it
> > + - Patch 2: drm: convert core ioctls from DRM_UNLOCKED to DRM_LOCKED
> > + - Patch 3-...: drm/driverX: convert driver ioctls from ...
> > + - Patch X: drm: remove no longer used DRM_UNLOCKED, drop todo item
> 
> Seems like too much bother for legacy drivers ... What I'd do is something
> a lot cheaper, since all we're touching here are legacy drivers:
> 
> Remove DRM_UNLOCKED from everything except the old vblank ioctl. That one
> we need to keep, because it freezes X:
> 
> commit 8f4ff2b06afcd6f151868474a432c603057eaf56
> Author: Ilija Hadzic <ihadzic at research.bell-labs.com>
> Date:   Mon Oct 31 17:46:18 2011 -0400
> 
>     drm: do not sleep on vblank while holding a mutex
> 
> Anything else I think is either never used by legacy userspace, or just
> doesn't matter. That's simple enough that I don't think we really need a
> todo for it :-) I guess if you want to kill DRM_UNLOCKED you could replace
> the check with ioctl->func == drm_vblank_ioctl, ofc only in the
> DRIVER_LEGACY path.
> 
Sounds like a much simpler solution indeed. Sadly I don't have much time to
double-check that this won't cause problems elsewhere, so I'll leave it that
to someone else.

> On patches 1-3 in your series:
> 
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> 
Thank you very much.

-Emil