Re: [PATCH v3 04/27] drm: Don't test for IRQ support in VBLANK ioctls

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Hi

Am 24.06.21 um 10:51 schrieb Jani Nikula:
> On Thu, 24 Jun 2021, Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
> > Hi
> >
> > Am 24.06.21 um 10:06 schrieb Jani Nikula:
> > > On Thu, 24 Jun 2021, Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
> > > > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> > > > index 3417e1ac7918..10fe16bafcb6 100644
> > > > --- a/drivers/gpu/drm/drm_vblank.c
> > > > +++ b/drivers/gpu/drm/drm_vblank.c
> > > > @@ -1748,8 +1748,16 @@ int drm_wait_vblank_ioctl(struct drm_device *dev, void *data,
> > > >    	unsigned int pipe_index;
> > > >    	unsigned int flags, pipe, high_pipe;
> > > >    
> > > > -	if (!dev->irq_enabled)
> > > > -		return -EOPNOTSUPP;
> > > > +#if defined(CONFIG_DRM_LEGACY)
> > > > +	if  (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY))) {
> > > > +		if (!dev->irq_enabled)
> > > > +			return -EOPNOTSUPP;
> > > > +	} else /* if DRIVER_MODESET */
> > > > +#endif
> > > > +	{
> > > > +		if (!drm_dev_has_vblank(dev))
> > > > +			return -EOPNOTSUPP;
> > > > +	}
> > >
> > > Sheesh I hate this kind of inline #ifdefs.
> > >
> > > Two alternate suggestions that I believe should be as just efficient:
> >
> > Or how about:
> >
> > static bool drm_wait_vblank_supported(struct drm_device *dev)
> >
> > {
> >
> > if defined(CONFIG_DRM_LEGACY)
> > 	if  (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)))
> >
> > 		return dev->irq_enabled;
> >
> > #endif
> > 	return drm_dev_has_vblank(dev);
> >
> > }
> >
> >
> > ?
> >
> > It's inline, but still readable.
>
> It's definitely better than the original, but it's unclear to me why
> you'd prefer this over option 2) below. I guess the only reason I can
> think of is emphasizing the conditional compilation. However,
> IS_ENABLED() is widely used in this manner specifically to avoid inline
> #if, and the compiler optimizes it away.

It's simply more readable to me as the condition is simpler. But option 
2 is also ok.

Best regards
Thomas

> BR,
> Jani.
>
>
> > Best regards
> > Thomas
> >
> > > 1) The more verbose:
> > >
> > > #if defined(CONFIG_DRM_LEGACY)
> > > static bool drm_wait_vblank_supported(struct drm_device *dev)
> > > {
> > > 	if  (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)))
> > > 		return dev->irq_enabled;
> > > 	else
> > > 		return drm_dev_has_vblank(dev);
> > > }
> > > #else
> > > static bool drm_wait_vblank_supported(struct drm_device *dev)
> > > {
> > > 	return drm_dev_has_vblank(dev);
> > > }
> > > #endif
> > >
> > > 2) The more compact:
> > >
> > > static bool drm_wait_vblank_supported(struct drm_device *dev)
> > > {
> > > 	if  (IS_ENABLED(CONFIG_DRM_LEGACY) && unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)))
> > > 		return dev->irq_enabled;
> > > 	else
> > > 		return drm_dev_has_vblank(dev);
> > > }
> > >
> > > Then, in drm_wait_vblank_ioctl().
> > >
> > > 	if (!drm_wait_vblank_supported(dev))
> > > 		return -EOPNOTSUPP;
> > >
> > > The compiler should do the right thing without any explicit inline
> > > keywords etc.
> > >
> > > BR,
> > > Jani.
> > >
> > > >    
> > > >    	if (vblwait->request.type & _DRM_VBLANK_SIGNAL)
> > > >    		return -EINVAL;
> > > > @@ -2023,7 +2031,7 @@ int drm_crtc_get_sequence_ioctl(struct drm_device *dev, void *data,
> > > >    	if (!drm_core_check_feature(dev, DRIVER_MODESET))
> > > >    		return -EOPNOTSUPP;
> > > >    
> > > > -	if (!dev->irq_enabled)
> > > > +	if (!drm_dev_has_vblank(dev))
> > > >    		return -EOPNOTSUPP;
> > > >    
> > > >    	crtc = drm_crtc_find(dev, file_priv, get_seq->crtc_id);
> > > > @@ -2082,7 +2090,7 @@ int drm_crtc_queue_sequence_ioctl(struct drm_device *dev, void *data,
> > > >    	if (!drm_core_check_feature(dev, DRIVER_MODESET))
> > > >    		return -EOPNOTSUPP;
> > > >    
> > > > -	if (!dev->irq_enabled)
> > > > +	if (!drm_dev_has_vblank(dev))
> > > >    		return -EOPNOTSUPP;
> > > >    
> > > >    	crtc = drm_crtc_find(dev, file_priv, queue_seq->crtc_id);

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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