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

Jani Nikula
2021-06-24T08:07:12Z

On Thu, 24 Jun 2021, Thomas Zimmermann <tzimmermann@suse.de> wrote:
> For KMS drivers, replace the IRQ check in VBLANK ioctls with a check for
> vblank support. IRQs might be enabled wthout vblanking being supported.
>
> This change also removes the DRM framework's only dependency on IRQ state
> for non-legacy drivers. For legacy drivers with userspace modesetting,
> the original test remains in drm_wait_vblank_ioctl().
>
> v3:
> * optimize test in drm_wait_vblank_ioctl() for KMS case (Liviu)
> * update docs for drm_irq_uninstall()
> v2:
> * keep the old test for legacy drivers in
> drm_wait_vblank_ioctl() (Daniel)
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
> drivers/gpu/drm/drm_irq.c | 13 ++++---------
> drivers/gpu/drm/drm_vblank.c | 16 ++++++++++++----
> 2 files changed, 16 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index c3bd664ea733..945dd82e2ea3 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.
> @@ -156,8 +152,7 @@ EXPORT_SYMBOL(drm_irq_install);
> *
> * Calls the driver's &drm_driver.irq_uninstall function and unregisters the IRQ
> * handler. This should only be called by drivers which used drm_irq_install()
> - * to set up their interrupt handler. Other drivers must only reset
> - * &drm_device.irq_enabled to false.
> + * to set up their interrupt handler.
> *
> * Note that for kernel modesetting drivers it is a bug if this function fails.
> * The sanity checks are only to catch buggy user modesetting drivers which call
> 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:

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);

--
Jani Nikula, Intel Open Source Graphics Center