[Intel-gfx] [PATCH v2 02/21] drm: Evaluate struct drm_device.vblank_disable_immediate on each use

[Thomas Zimmermann]

Hi

Am 15.01.20 um 15:37 schrieb Ville Syrjälä:
> On Wed, Jan 15, 2020 at 01:16:33PM +0100, Thomas Zimmermann wrote:
>> VBLANK interrupts can be disabled immediately or with a delay, where the
>> latter is the default. The former option can be selected by setting
>> get_vblank_timestamp, and enabling vblank_disable_immediate in struct
>> drm_device.
>>
>> The setup is only evaluated once when DRM initializes VBLANKs. Evaluating
>> the settings on each use of vblank_disable_immediate will allow for easy
>> integration of CRTC VBLANK functions.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
>> ---
>>  drivers/gpu/drm/drm_vblank.c | 31 ++++++++++++++-----------------
>>  1 file changed, 14 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
>> index 3f1dd54cc8bb..abb085c67d82 100644
>> --- a/drivers/gpu/drm/drm_vblank.c
>> +++ b/drivers/gpu/drm/drm_vblank.c
>> @@ -481,19 +481,6 @@ int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs)
>>  
>>  	DRM_INFO("Supports vblank timestamp caching Rev 2 (21.10.2013).\n");
>>  
>> -	/* Driver specific high-precision vblank timestamping supported? */
>> -	if (dev->driver->get_vblank_timestamp)
>> -		DRM_INFO("Driver supports precise vblank timestamp query.\n");
>> -	else
>> -		DRM_INFO("No driver support for vblank timestamp query.\n");
>> -
>> -	/* Must have precise timestamping for reliable vblank instant disable */
>> -	if (dev->vblank_disable_immediate && !dev->driver->get_vblank_timestamp) {
>> -		dev->vblank_disable_immediate = false;
>> -		DRM_INFO("Setting vblank_disable_immediate to false because "
>> -			 "get_vblank_timestamp == NULL\n");
>> -	}
> 
> Which drivers are so broken they set vblank_disable_immediate to true
> without having the vfunc specified? IMO this code should just go away
> (or converted to a WARN).

It's probably not a problem in practice. I'll put WARN_ON around the
condition.

Best regards
Thomas

> 
>> -
>>  	return 0;
>>  
>>  err:
>> @@ -1070,6 +1057,15 @@ int drm_crtc_vblank_get(struct drm_crtc *crtc)
>>  }
>>  EXPORT_SYMBOL(drm_crtc_vblank_get);
>>  
>> +static bool __vblank_disable_immediate(struct drm_device *dev, unsigned int pipe)
>> +{
>> +	if (!dev->vblank_disable_immediate)
>> +		return false;
>> +	if (!dev->driver->get_vblank_timestamp)
>> +		return false;
>> +	return true;
>> +}
>> +
>>  static void drm_vblank_put(struct drm_device *dev, unsigned int pipe)
>>  {
>>  	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
>> @@ -1086,7 +1082,7 @@ static void drm_vblank_put(struct drm_device *dev, unsigned int pipe)
>>  			return;
>>  		else if (drm_vblank_offdelay < 0)
>>  			vblank_disable_fn(&vblank->disable_timer);
>> -		else if (!dev->vblank_disable_immediate)
>> +		else if (__vblank_disable_immediate(dev, pipe))
>>  			mod_timer(&vblank->disable_timer,
>>  				  jiffies + ((drm_vblank_offdelay * HZ)/1000));
>>  	}
>> @@ -1663,7 +1659,7 @@ int drm_wait_vblank_ioctl(struct drm_device *dev, void *data,
>>  	/* If the counter is currently enabled and accurate, short-circuit
>>  	 * queries to return the cached timestamp of the last vblank.
>>  	 */
>> -	if (dev->vblank_disable_immediate &&
>> +	if (__vblank_disable_immediate(dev, pipe) &&
>>  	    drm_wait_vblank_is_query(vblwait) &&
>>  	    READ_ONCE(vblank->enabled)) {
>>  		drm_wait_vblank_reply(dev, pipe, &vblwait->reply);
>> @@ -1820,7 +1816,7 @@ bool drm_handle_vblank(struct drm_device *dev, unsigned int pipe)
>>  	 * been signaled. The disable has to be last (after
>>  	 * drm_handle_vblank_events) so that the timestamp is always accurate.
>>  	 */
>> -	disable_irq = (dev->vblank_disable_immediate &&
>> +	disable_irq = (__vblank_disable_immediate(dev, pipe) &&
>>  		       drm_vblank_offdelay > 0 &&
>>  		       !atomic_read(&vblank->refcount));
>>  
>> @@ -1893,7 +1889,8 @@ int drm_crtc_get_sequence_ioctl(struct drm_device *dev, void *data,
>>  	pipe = drm_crtc_index(crtc);
>>  
>>  	vblank = &dev->vblank[pipe];
>> -	vblank_enabled = dev->vblank_disable_immediate && READ_ONCE(vblank->enabled);
>> +	vblank_enabled = __vblank_disable_immediate(dev, pipe) &&
>> +			 READ_ONCE(vblank->enabled);
>>  
>>  	if (!vblank_enabled) {
>>  		ret = drm_crtc_vblank_get(crtc);
>> -- 
>> 2.24.1
>>
>> _______________________________________________
>> Intel-gfx mailing list
>> Intel-gfx at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 

-- 
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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