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

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Hi

Am 24.06.21 um 10:06 schrieb Jani Nikula:
On Thu, 24 Jun 2021, Thomas Zimmermann <tzimmermann@xxxxxxx> 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@xxxxxxx>
Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
---
  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.

I don't like them either. I guess I'll go with suggestion 2. Thanks for the feedback.

Best regards
Thomas


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);


--
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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