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

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Jun 08, 2021 at 11:03:01AM +0200, Thomas Zimmermann wrote:
> Replace the IRQ check in VBLANK ioctls with a check for vblank
> support. IRQs might be enabled wthout vblanking being supported.

Nah, or if they are, that's a broken driver. irq_enabled here really only
means vblank_irq_enabled (maybe we should rename it). I'd like to
understand the motivation here a bit better to make sure we'r not just
papering over a driver bug.

Also as-is this breaks legacy drivers, which do enable/disable irqs at
runtime with the legacy IRQ_CONTROL ioctl, so we can't just throw this
out. Hence this cleanup here is only ok for non-legacy drivers.

Finally if you do this cleanup I think we should go through drivers and
drop the irq_enabled = true settings that are littered around. For that
cleanup I think this patch makes sense.
-Daniel
> 
> This change also removes the DRM framework's only dependency on
> IRQ state for non-legacy drivers.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
>  drivers/gpu/drm/drm_irq.c    | 10 +++-------
>  drivers/gpu/drm/drm_vblank.c |  6 +++---
>  2 files changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index c3bd664ea733..1d7785721323 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -74,10 +74,8 @@
>   * only supports devices with a single interrupt on the main device stored in
>   * &drm_device.dev and set as the device paramter in drm_dev_alloc().
>   *
> - * These IRQ helpers are strictly optional. Drivers which roll their own only
> - * need to set &drm_device.irq_enabled to signal the DRM core that vblank
> - * interrupts are working. Since these helpers don't automatically clean up the
> - * requested interrupt like e.g. devm_request_irq() they're not really
> + * These IRQ helpers are strictly optional. Since these helpers don't automatically
> + * clean up the requested interrupt like e.g. devm_request_irq() they're not really
>   * recommended.
>   */
>  
> @@ -91,9 +89,7 @@
>   * and after the installation.
>   *
>   * This is the simplified helper interface provided for drivers with no special
> - * needs. Drivers which need to install interrupt handlers for multiple
> - * interrupts must instead set &drm_device.irq_enabled to signal the DRM core
> - * that vblank interrupts are available.
> + * needs.
>   *
>   * @irq must match the interrupt number that would be passed to request_irq(),
>   * if called directly instead of using this helper function.
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 3417e1ac7918..165286fef478 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -1748,7 +1748,7 @@ 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)
> +	if (!drm_dev_has_vblank(dev))
>  		return -EOPNOTSUPP;
>  
>  	if (vblwait->request.type & _DRM_VBLANK_SIGNAL)
> @@ -2023,7 +2023,7 @@ 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 +2082,7 @@ 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);
> -- 
> 2.31.1
> 

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