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

From: Daniel Vetter <daniel@ffwll.ch>
To: Emil Velikov <emil.l.velikov@gmail.com>
Cc: kernel@collabora.com, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH 4/4] drm/TODO: add a task to kill DRM_UNLOCKED
Date: Fri, 24 May 2019 17:59:40 +0200	[thread overview]
Message-ID: <20190524155940.GA21222@phenom.ffwll.local> (raw)
In-Reply-To: <20190524151716.GB8938@arch-x1c3>

On Fri, May 24, 2019 at 04:17:16PM +0100, Emil Velikov wrote:
> 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@collabora.com>
> > > 
> > > Should minimise the copy/paste mistakes, fixed with previous patches.
> > > 
> > > Cc: Daniel Vetter <daniel@ffwll.ch>
> > > Signed-off-by: Emil Velikov <emil.velikov@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@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.

I did dig through enough history that I'm confident. I'll type a patch and
some awkward-long commit message :-)
-Daniel

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

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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