Re: [PATCH 3/5] drm: Allow the driver to reject vblank requests only when it really has the vblank interrupts disabled

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Mar 04, 2014 at 10:24:54AM +0100, Daniel Vetter wrote:
> On Fri, Feb 21, 2014 at 09:03:33PM +0200, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Allow the driver to specify whether all new vblank requests after
> > drm_vblank_off() should be rejected. And add a counterpart called
> > drm_vblank_on() which will again allow vblank requests to come in.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Not really happy about this - drm_irq.c is already a giant mess, adding
> more driver-specific hacks doesn't help. I think we need a few bits of
> polish on top of your code:
> 
> - Add stern warnings to pre/post_modeset that they're inherently racy.
> 
> - Add calls to drm_vblank_off to every driver lacking them. Put it at the
>   beginning of their crtc disable functions expect when there's a call to
>   pre_modeset. Then it should be right after that.
> 
> - Sprinkle calls to drm_vblank_on over all drivers. Put them at the end of
>   their crtc enable functions except when there's a call to post_modeset.
>   Then put it right before that.
> 
> - Rip out the reject argument again and make it the default. If we have
>   drm_vblank_off everywhere then all old vblank waits should complete and
>   there's no userspace yet out there which races a modeset with vblank
>   ioctl calls. Then only issue would be userspace which does vblank waits
>   on disabled ioctls which a) is buggy b) we can easily fix with a driver
>   quirk flag if _really_ needed.
> 
> This way the drm_irq.c mess will at least converge a bit and so should
> help generic display servers (like Wayland) a lot.
> 
> I can volunteer for this if you want to punt on it yourself.

Much appreciated. I'll punt.

My hope was that other people would fix their own mess after seeing how
i915 did it, and then we could rip out the crap, but if you're feeling
the urge to do it all upfront I certainly won't object.

-- 
Ville Syrjälä
Intel OTC