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

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 24.06.21 um 10:06 schrieb Jani Nikula:
> 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.

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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