Nouveau - Jan 2020 - [PATCH 03/23] drm/i915: Don't use struct drm_driver.get_scanout_position()

On Fri, 10 Jan 2020, Thomas Zimmermann <tzimmermann at suse.de>
wrote:
> The callback struct drm_driver.get_scanout_position() is deprecated in
> favor of struct drm_crtc_helper_funcs.get_scanout_position().
>
> i915 doesn't use CRTC helpers. The patch duplicates the caller
> drm_calc_vbltimestamp_from_scanoutpos() for i915, such that the callback
> function is not needed.
>
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> ---
>  drivers/gpu/drm/i915/i915_drv.c |   3 +-
>  drivers/gpu/drm/i915/i915_irq.c | 117 ++++++++++++++++++++++++++++++--
>  drivers/gpu/drm/i915/i915_irq.h |   9 +--
>  3 files changed, 119 insertions(+), 10 deletions(-)
Not really enthusiastic about the diffstat in a "cleanup" series.

I wonder if you could add a generic helper version of
drm_calc_vbltimestamp_from_scanoutpos where you pass the
get_scanout_position function as a parameter. Both
drm_calc_vbltimestamp_from_scanoutpos and the new
i915_calc_vbltimestamp_from_scanoutpos would then be fairly thin
wrappers passing in the relevant get_scanout_position function.

This would reduce the almost identical duplication of the function in
i915.

BR,
Jani.
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.c
b/drivers/gpu/drm/i915/i915_drv.c
> index f7385abdd74b..4a0a7fb85c53 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -2769,8 +2769,7 @@ static struct drm_driver driver = {
>  	.gem_prime_export = i915_gem_prime_export,
>  	.gem_prime_import = i915_gem_prime_import,
>  
> -	.get_vblank_timestamp = drm_calc_vbltimestamp_from_scanoutpos,
> -	.get_scanout_position = i915_get_crtc_scanoutpos,
> +	.get_vblank_timestamp = i915_calc_vbltimestamp_from_scanoutpos,
>  
>  	.dumb_create = i915_gem_dumb_create,
>  	.dumb_map_offset = i915_gem_dumb_mmap_offset,
> diff --git a/drivers/gpu/drm/i915/i915_irq.c
b/drivers/gpu/drm/i915/i915_irq.c
> index afc6aad9bf8c..99d0c3b0feae 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -52,6 +52,11 @@
>  #include "i915_trace.h"
>  #include "intel_pm.h"
>  
> +/* Retry timestamp calculation up to 3 times to satisfy
> + * drm_timestamp_precision before giving up.
> + */
> +#define I915_TIMESTAMP_MAXRETRIES 3
> +
>  /**
>   * DOC: interrupt handling
>   *
> @@ -762,10 +767,11 @@ static int __intel_get_crtc_scanline(struct
intel_crtc *crtc)
>  	return (position + crtc->scanline_offset) % vtotal;
>  }
>  
> -bool i915_get_crtc_scanoutpos(struct drm_device *dev, unsigned int index,
> -			      bool in_vblank_irq, int *vpos, int *hpos,
> -			      ktime_t *stime, ktime_t *etime,
> -			      const struct drm_display_mode *mode)
> +static bool i915_get_crtc_scanoutpos(struct drm_device *dev,
> +				     unsigned int index, bool in_vblank_irq,
> +				     int *vpos, int *hpos,
> +				     ktime_t *stime, ktime_t *etime,
> +				     const struct drm_display_mode *mode)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(dev);
>  	struct intel_crtc *crtc = to_intel_crtc(drm_crtc_from_index(dev, index));
> @@ -879,6 +885,109 @@ bool i915_get_crtc_scanoutpos(struct drm_device *dev,
unsigned int index,
>  	return true;
>  }
>  
> +bool i915_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
> +					    unsigned int pipe,
> +					    int *max_error,
> +					    ktime_t *vblank_time,
> +					    bool in_vblank_irq)
> +{
> +	struct timespec64 ts_etime, ts_vblank_time;
> +	ktime_t stime, etime;
> +	bool vbl_status;
> +	struct drm_crtc *crtc;
> +	const struct drm_display_mode *mode;
> +	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> +	int vpos, hpos, i;
> +	int delta_ns, duration_ns;
> +
> +	crtc = drm_crtc_from_index(dev, pipe);
> +
> +	if (pipe >= dev->num_crtcs || !crtc) {
> +		DRM_ERROR("Invalid crtc %u\n", pipe);
> +		return false;
> +	}
> +
> +	if (drm_drv_uses_atomic_modeset(dev))
> +		mode = &vblank->hwmode;
> +	else
> +		mode = &crtc->hwmode;
> +
> +	/* If mode timing undefined, just return as no-op:
> +	 * Happens during initial modesetting of a crtc.
> +	 */
> +	if (mode->crtc_clock == 0) {
> +		DRM_DEBUG("crtc %u: Noop due to uninitialized mode.\n", pipe);
> +		WARN_ON_ONCE(drm_drv_uses_atomic_modeset(dev));
> +
> +		return false;
> +	}
> +
> +	/* Get current scanout position with system timestamp.
> +	 * Repeat query up to DRM_TIMESTAMP_MAXRETRIES times
> +	 * if single query takes longer than max_error nanoseconds.
> +	 *
> +	 * This guarantees a tight bound on maximum error if
> +	 * code gets preempted or delayed for some reason.
> +	 */
> +	for (i = 0; i < I915_TIMESTAMP_MAXRETRIES; i++) {
> +		/*
> +		 * Get vertical and horizontal scanout position vpos, hpos,
> +		 * and bounding timestamps stime, etime, pre/post query.
> +		 */
> +		vbl_status = i915_get_crtc_scanoutpos(dev, pipe, in_vblank_irq,
> +						      &vpos, &hpos, &stime,
> +						      &etime, mode);
> +		/* Return as no-op if scanout query unsupported or failed. */
> +		if (!vbl_status) {
> +			DRM_DEBUG("crtc %u : scanoutpos query failed.\n",
> +				  pipe);
> +			return false;
> +		}
> +
> +		/* Compute uncertainty in timestamp of scanout position query. */
> +		duration_ns = ktime_to_ns(etime) - ktime_to_ns(stime);
> +
> +		/* Accept result with <  max_error nsecs timing uncertainty. */
> +		if (duration_ns <= *max_error)
> +			break;
> +	}
> +
> +	/* Noisy system timing? */
> +	if (i == I915_TIMESTAMP_MAXRETRIES) {
> +		DRM_DEBUG("crtc %u: Noisy timestamp %d us > %d us [%d
reps].\n",
> +			  pipe, duration_ns/1000, *max_error/1000, i);
> +	}
> +
> +	/* Return upper bound of timestamp precision error. */
> +	*max_error = duration_ns;
> +
> +	/* Convert scanout position into elapsed time at raw_time query
> +	 * since start of scanout at first display scanline. delta_ns
> +	 * can be negative if start of scanout hasn't happened yet.
> +	 */
> +	delta_ns = div_s64(1000000LL * (vpos * mode->crtc_htotal + hpos),
> +			   mode->crtc_clock);
> +
> +	/* Subtract time delta from raw timestamp to get final
> +	 * vblank_time timestamp for end of vblank.
> +	 */
> +	*vblank_time = ktime_sub_ns(etime, delta_ns);
> +
> +	if (!drm_debug_enabled(DRM_UT_VBL))
> +		return true;
> +
> +	ts_etime = ktime_to_timespec64(etime);
> +	ts_vblank_time = ktime_to_timespec64(*vblank_time);
> +
> +	DRM_DEBUG_VBL("crtc %u : v p(%d,%d)@ %lld.%06ld -> %lld.%06ld [e
%d us, %d rep]\n",
> +		      pipe, hpos, vpos,
> +		      (u64)ts_etime.tv_sec, ts_etime.tv_nsec / 1000,
> +		      (u64)ts_vblank_time.tv_sec, ts_vblank_time.tv_nsec / 1000,
> +		      duration_ns / 1000, i);
> +
> +	return true;
> +}
> +
>  int intel_get_crtc_scanline(struct intel_crtc *crtc)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
> diff --git a/drivers/gpu/drm/i915/i915_irq.h
b/drivers/gpu/drm/i915/i915_irq.h
> index 812c47a9c2d6..5f7b133ce721 100644
> --- a/drivers/gpu/drm/i915/i915_irq.h
> +++ b/drivers/gpu/drm/i915/i915_irq.h
> @@ -101,10 +101,11 @@ void gen8_irq_power_well_post_enable(struct
drm_i915_private *dev_priv,
>  void gen8_irq_power_well_pre_disable(struct drm_i915_private *dev_priv,
>  				     u8 pipe_mask);
>  
> -bool i915_get_crtc_scanoutpos(struct drm_device *dev, unsigned int pipe,
> -			      bool in_vblank_irq, int *vpos, int *hpos,
> -			      ktime_t *stime, ktime_t *etime,
> -			      const struct drm_display_mode *mode);
> +bool i915_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
> +					    unsigned int pipe,
> +					    int *max_error,
> +					    ktime_t *vblank_time,
> +					    bool in_vblank_irq);
>  
>  u32 i915_get_vblank_counter(struct drm_crtc *crtc);
>  u32 g4x_get_vblank_counter(struct drm_crtc *crtc);
-- 
Jani Nikula, Intel Open Source Graphics Center

Hi

Am 10.01.20 um 12:59 schrieb Jani Nikula:
> On Fri, 10 Jan 2020, Thomas Zimmermann <tzimmermann at suse.de>
wrote:
>> The callback struct drm_driver.get_scanout_position() is deprecated in
>> favor of struct drm_crtc_helper_funcs.get_scanout_position().
>>
>> i915 doesn't use CRTC helpers. The patch duplicates the caller
>> drm_calc_vbltimestamp_from_scanoutpos() for i915, such that the
callback
>> function is not needed.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
>> ---
>>  drivers/gpu/drm/i915/i915_drv.c |   3 +-
>>  drivers/gpu/drm/i915/i915_irq.c | 117 ++++++++++++++++++++++++++++++--
>>  drivers/gpu/drm/i915/i915_irq.h |   9 +--
>>  3 files changed, 119 insertions(+), 10 deletions(-)
> 
> Not really enthusiastic about the diffstat in a "cleanup" series.
Well, the cleanup is about the content of drm_driver :)
> 
> I wonder if you could add a generic helper version of
> drm_calc_vbltimestamp_from_scanoutpos where you pass the
> get_scanout_position function as a parameter. Both
> drm_calc_vbltimestamp_from_scanoutpos and the new
> i915_calc_vbltimestamp_from_scanoutpos would then be fairly thin
> wrappers passing in the relevant get_scanout_position function.
Of course. Will be in v2 of the series.

Best regards
Thomas
> 
> This would reduce the almost identical duplication of the function in
> i915.
> 
> BR,
> Jani.
> 
>>
>> diff --git a/drivers/gpu/drm/i915/i915_drv.c
b/drivers/gpu/drm/i915/i915_drv.c
>> index f7385abdd74b..4a0a7fb85c53 100644
>> --- a/drivers/gpu/drm/i915/i915_drv.c
>> +++ b/drivers/gpu/drm/i915/i915_drv.c
>> @@ -2769,8 +2769,7 @@ static struct drm_driver driver = {
>>  	.gem_prime_export = i915_gem_prime_export,
>>  	.gem_prime_import = i915_gem_prime_import,
>>  
>> -	.get_vblank_timestamp = drm_calc_vbltimestamp_from_scanoutpos,
>> -	.get_scanout_position = i915_get_crtc_scanoutpos,
>> +	.get_vblank_timestamp = i915_calc_vbltimestamp_from_scanoutpos,
>>  
>>  	.dumb_create = i915_gem_dumb_create,
>>  	.dumb_map_offset = i915_gem_dumb_mmap_offset,
>> diff --git a/drivers/gpu/drm/i915/i915_irq.c
b/drivers/gpu/drm/i915/i915_irq.c
>> index afc6aad9bf8c..99d0c3b0feae 100644
>> --- a/drivers/gpu/drm/i915/i915_irq.c
>> +++ b/drivers/gpu/drm/i915/i915_irq.c
>> @@ -52,6 +52,11 @@
>>  #include "i915_trace.h"
>>  #include "intel_pm.h"
>>  
>> +/* Retry timestamp calculation up to 3 times to satisfy
>> + * drm_timestamp_precision before giving up.
>> + */
>> +#define I915_TIMESTAMP_MAXRETRIES 3
>> +
>>  /**
>>   * DOC: interrupt handling
>>   *
>> @@ -762,10 +767,11 @@ static int __intel_get_crtc_scanline(struct
intel_crtc *crtc)
>>  	return (position + crtc->scanline_offset) % vtotal;
>>  }
>>  
>> -bool i915_get_crtc_scanoutpos(struct drm_device *dev, unsigned int
index,
>> -			      bool in_vblank_irq, int *vpos, int *hpos,
>> -			      ktime_t *stime, ktime_t *etime,
>> -			      const struct drm_display_mode *mode)
>> +static bool i915_get_crtc_scanoutpos(struct drm_device *dev,
>> +				     unsigned int index, bool in_vblank_irq,
>> +				     int *vpos, int *hpos,
>> +				     ktime_t *stime, ktime_t *etime,
>> +				     const struct drm_display_mode *mode)
>>  {
>>  	struct drm_i915_private *dev_priv = to_i915(dev);
>>  	struct intel_crtc *crtc = to_intel_crtc(drm_crtc_from_index(dev,
index));
>> @@ -879,6 +885,109 @@ bool i915_get_crtc_scanoutpos(struct drm_device
*dev, unsigned int index,
>>  	return true;
>>  }
>>  
>> +bool i915_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
>> +					    unsigned int pipe,
>> +					    int *max_error,
>> +					    ktime_t *vblank_time,
>> +					    bool in_vblank_irq)
>> +{
>> +	struct timespec64 ts_etime, ts_vblank_time;
>> +	ktime_t stime, etime;
>> +	bool vbl_status;
>> +	struct drm_crtc *crtc;
>> +	const struct drm_display_mode *mode;
>> +	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
>> +	int vpos, hpos, i;
>> +	int delta_ns, duration_ns;
>> +
>> +	crtc = drm_crtc_from_index(dev, pipe);
>> +
>> +	if (pipe >= dev->num_crtcs || !crtc) {
>> +		DRM_ERROR("Invalid crtc %u\n", pipe);
>> +		return false;
>> +	}
>> +
>> +	if (drm_drv_uses_atomic_modeset(dev))
>> +		mode = &vblank->hwmode;
>> +	else
>> +		mode = &crtc->hwmode;
>> +
>> +	/* If mode timing undefined, just return as no-op:
>> +	 * Happens during initial modesetting of a crtc.
>> +	 */
>> +	if (mode->crtc_clock == 0) {
>> +		DRM_DEBUG("crtc %u: Noop due to uninitialized mode.\n",
pipe);
>> +		WARN_ON_ONCE(drm_drv_uses_atomic_modeset(dev));
>> +
>> +		return false;
>> +	}
>> +
>> +	/* Get current scanout position with system timestamp.
>> +	 * Repeat query up to DRM_TIMESTAMP_MAXRETRIES times
>> +	 * if single query takes longer than max_error nanoseconds.
>> +	 *
>> +	 * This guarantees a tight bound on maximum error if
>> +	 * code gets preempted or delayed for some reason.
>> +	 */
>> +	for (i = 0; i < I915_TIMESTAMP_MAXRETRIES; i++) {
>> +		/*
>> +		 * Get vertical and horizontal scanout position vpos, hpos,
>> +		 * and bounding timestamps stime, etime, pre/post query.
>> +		 */
>> +		vbl_status = i915_get_crtc_scanoutpos(dev, pipe, in_vblank_irq,
>> +						      &vpos, &hpos, &stime,
>> +						      &etime, mode);
>> +		/* Return as no-op if scanout query unsupported or failed. */
>> +		if (!vbl_status) {
>> +			DRM_DEBUG("crtc %u : scanoutpos query failed.\n",
>> +				  pipe);
>> +			return false;
>> +		}
>> +
>> +		/* Compute uncertainty in timestamp of scanout position query. */
>> +		duration_ns = ktime_to_ns(etime) - ktime_to_ns(stime);
>> +
>> +		/* Accept result with <  max_error nsecs timing uncertainty. */
>> +		if (duration_ns <= *max_error)
>> +			break;
>> +	}
>> +
>> +	/* Noisy system timing? */
>> +	if (i == I915_TIMESTAMP_MAXRETRIES) {
>> +		DRM_DEBUG("crtc %u: Noisy timestamp %d us > %d us [%d
reps].\n",
>> +			  pipe, duration_ns/1000, *max_error/1000, i);
>> +	}
>> +
>> +	/* Return upper bound of timestamp precision error. */
>> +	*max_error = duration_ns;
>> +
>> +	/* Convert scanout position into elapsed time at raw_time query
>> +	 * since start of scanout at first display scanline. delta_ns
>> +	 * can be negative if start of scanout hasn't happened yet.
>> +	 */
>> +	delta_ns = div_s64(1000000LL * (vpos * mode->crtc_htotal + hpos),
>> +			   mode->crtc_clock);
>> +
>> +	/* Subtract time delta from raw timestamp to get final
>> +	 * vblank_time timestamp for end of vblank.
>> +	 */
>> +	*vblank_time = ktime_sub_ns(etime, delta_ns);
>> +
>> +	if (!drm_debug_enabled(DRM_UT_VBL))
>> +		return true;
>> +
>> +	ts_etime = ktime_to_timespec64(etime);
>> +	ts_vblank_time = ktime_to_timespec64(*vblank_time);
>> +
>> +	DRM_DEBUG_VBL("crtc %u : v p(%d,%d)@ %lld.%06ld -> %lld.%06ld
[e %d us, %d rep]\n",
>> +		      pipe, hpos, vpos,
>> +		      (u64)ts_etime.tv_sec, ts_etime.tv_nsec / 1000,
>> +		      (u64)ts_vblank_time.tv_sec, ts_vblank_time.tv_nsec / 1000,
>> +		      duration_ns / 1000, i);
>> +
>> +	return true;
>> +}
>> +
>>  int intel_get_crtc_scanline(struct intel_crtc *crtc)
>>  {
>>  	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
>> diff --git a/drivers/gpu/drm/i915/i915_irq.h
b/drivers/gpu/drm/i915/i915_irq.h
>> index 812c47a9c2d6..5f7b133ce721 100644
>> --- a/drivers/gpu/drm/i915/i915_irq.h
>> +++ b/drivers/gpu/drm/i915/i915_irq.h
>> @@ -101,10 +101,11 @@ void gen8_irq_power_well_post_enable(struct
drm_i915_private *dev_priv,
>>  void gen8_irq_power_well_pre_disable(struct drm_i915_private
*dev_priv,
>>  				     u8 pipe_mask);
>>  
>> -bool i915_get_crtc_scanoutpos(struct drm_device *dev, unsigned int
pipe,
>> -			      bool in_vblank_irq, int *vpos, int *hpos,
>> -			      ktime_t *stime, ktime_t *etime,
>> -			      const struct drm_display_mode *mode);
>> +bool i915_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
>> +					    unsigned int pipe,
>> +					    int *max_error,
>> +					    ktime_t *vblank_time,
>> +					    bool in_vblank_irq);
>>  
>>  u32 i915_get_vblank_counter(struct drm_crtc *crtc);
>>  u32 g4x_get_vblank_counter(struct drm_crtc *crtc);
> 
-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 N?rnberg, Germany
(HRB 36809, AG N?rnberg)
Gesch?ftsf?hrer: Felix Imend?rffer

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On Fri, 10 Jan 2020, Thomas Zimmermann <tzimmermann at suse.de>
wrote:
> Hi
>
> Am 10.01.20 um 12:59 schrieb Jani Nikula:
>> On Fri, 10 Jan 2020, Thomas Zimmermann <tzimmermann at suse.de>
wrote:
>>> The callback struct drm_driver.get_scanout_position() is deprecated
in
>>> favor of struct drm_crtc_helper_funcs.get_scanout_position().
>>>
>>> i915 doesn't use CRTC helpers. The patch duplicates the caller
>>> drm_calc_vbltimestamp_from_scanoutpos() for i915, such that the
callback
>>> function is not needed.
>>>
>>> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
>>> ---
>>>  drivers/gpu/drm/i915/i915_drv.c |   3 +-
>>>  drivers/gpu/drm/i915/i915_irq.c | 117
++++++++++++++++++++++++++++++--
>>>  drivers/gpu/drm/i915/i915_irq.h |   9 +--
>>>  3 files changed, 119 insertions(+), 10 deletions(-)
>> 
>> Not really enthusiastic about the diffstat in a "cleanup"
series.
>
> Well, the cleanup is about the content of drm_driver :)
>
>> 
>> I wonder if you could add a generic helper version of
>> drm_calc_vbltimestamp_from_scanoutpos where you pass the
>> get_scanout_position function as a parameter. Both
>> drm_calc_vbltimestamp_from_scanoutpos and the new
>> i915_calc_vbltimestamp_from_scanoutpos would then be fairly thin
>> wrappers passing in the relevant get_scanout_position function.
>
> Of course. Will be in v2 of the series.
Please give Ville (Cc'd) a moment before sending v2 in case he wants to
chime in on this.

Thanks,
Jani.

>
> Best regards
> Thomas
>
>> 
>> This would reduce the almost identical duplication of the function in
>> i915.
>> 
>> BR,
>> Jani.
>> 
>>>
>>> diff --git a/drivers/gpu/drm/i915/i915_drv.c
b/drivers/gpu/drm/i915/i915_drv.c
>>> index f7385abdd74b..4a0a7fb85c53 100644
>>> --- a/drivers/gpu/drm/i915/i915_drv.c
>>> +++ b/drivers/gpu/drm/i915/i915_drv.c
>>> @@ -2769,8 +2769,7 @@ static struct drm_driver driver = {
>>>  	.gem_prime_export = i915_gem_prime_export,
>>>  	.gem_prime_import = i915_gem_prime_import,
>>>  
>>> -	.get_vblank_timestamp = drm_calc_vbltimestamp_from_scanoutpos,
>>> -	.get_scanout_position = i915_get_crtc_scanoutpos,
>>> +	.get_vblank_timestamp = i915_calc_vbltimestamp_from_scanoutpos,
>>>  
>>>  	.dumb_create = i915_gem_dumb_create,
>>>  	.dumb_map_offset = i915_gem_dumb_mmap_offset,
>>> diff --git a/drivers/gpu/drm/i915/i915_irq.c
b/drivers/gpu/drm/i915/i915_irq.c
>>> index afc6aad9bf8c..99d0c3b0feae 100644
>>> --- a/drivers/gpu/drm/i915/i915_irq.c
>>> +++ b/drivers/gpu/drm/i915/i915_irq.c
>>> @@ -52,6 +52,11 @@
>>>  #include "i915_trace.h"
>>>  #include "intel_pm.h"
>>>  
>>> +/* Retry timestamp calculation up to 3 times to satisfy
>>> + * drm_timestamp_precision before giving up.
>>> + */
>>> +#define I915_TIMESTAMP_MAXRETRIES 3
>>> +
>>>  /**
>>>   * DOC: interrupt handling
>>>   *
>>> @@ -762,10 +767,11 @@ static int __intel_get_crtc_scanline(struct
intel_crtc *crtc)
>>>  	return (position + crtc->scanline_offset) % vtotal;
>>>  }
>>>  
>>> -bool i915_get_crtc_scanoutpos(struct drm_device *dev, unsigned int
index,
>>> -			      bool in_vblank_irq, int *vpos, int *hpos,
>>> -			      ktime_t *stime, ktime_t *etime,
>>> -			      const struct drm_display_mode *mode)
>>> +static bool i915_get_crtc_scanoutpos(struct drm_device *dev,
>>> +				     unsigned int index, bool in_vblank_irq,
>>> +				     int *vpos, int *hpos,
>>> +				     ktime_t *stime, ktime_t *etime,
>>> +				     const struct drm_display_mode *mode)
>>>  {
>>>  	struct drm_i915_private *dev_priv = to_i915(dev);
>>>  	struct intel_crtc *crtc = to_intel_crtc(drm_crtc_from_index(dev,
index));
>>> @@ -879,6 +885,109 @@ bool i915_get_crtc_scanoutpos(struct
drm_device *dev, unsigned int index,
>>>  	return true;
>>>  }
>>>  
>>> +bool i915_calc_vbltimestamp_from_scanoutpos(struct drm_device
*dev,
>>> +					    unsigned int pipe,
>>> +					    int *max_error,
>>> +					    ktime_t *vblank_time,
>>> +					    bool in_vblank_irq)
>>> +{
>>> +	struct timespec64 ts_etime, ts_vblank_time;
>>> +	ktime_t stime, etime;
>>> +	bool vbl_status;
>>> +	struct drm_crtc *crtc;
>>> +	const struct drm_display_mode *mode;
>>> +	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
>>> +	int vpos, hpos, i;
>>> +	int delta_ns, duration_ns;
>>> +
>>> +	crtc = drm_crtc_from_index(dev, pipe);
>>> +
>>> +	if (pipe >= dev->num_crtcs || !crtc) {
>>> +		DRM_ERROR("Invalid crtc %u\n", pipe);
>>> +		return false;
>>> +	}
>>> +
>>> +	if (drm_drv_uses_atomic_modeset(dev))
>>> +		mode = &vblank->hwmode;
>>> +	else
>>> +		mode = &crtc->hwmode;
>>> +
>>> +	/* If mode timing undefined, just return as no-op:
>>> +	 * Happens during initial modesetting of a crtc.
>>> +	 */
>>> +	if (mode->crtc_clock == 0) {
>>> +		DRM_DEBUG("crtc %u: Noop due to uninitialized
mode.\n", pipe);
>>> +		WARN_ON_ONCE(drm_drv_uses_atomic_modeset(dev));
>>> +
>>> +		return false;
>>> +	}
>>> +
>>> +	/* Get current scanout position with system timestamp.
>>> +	 * Repeat query up to DRM_TIMESTAMP_MAXRETRIES times
>>> +	 * if single query takes longer than max_error nanoseconds.
>>> +	 *
>>> +	 * This guarantees a tight bound on maximum error if
>>> +	 * code gets preempted or delayed for some reason.
>>> +	 */
>>> +	for (i = 0; i < I915_TIMESTAMP_MAXRETRIES; i++) {
>>> +		/*
>>> +		 * Get vertical and horizontal scanout position vpos, hpos,
>>> +		 * and bounding timestamps stime, etime, pre/post query.
>>> +		 */
>>> +		vbl_status = i915_get_crtc_scanoutpos(dev, pipe, in_vblank_irq,
>>> +						      &vpos, &hpos, &stime,
>>> +						      &etime, mode);
>>> +		/* Return as no-op if scanout query unsupported or failed. */
>>> +		if (!vbl_status) {
>>> +			DRM_DEBUG("crtc %u : scanoutpos query failed.\n",
>>> +				  pipe);
>>> +			return false;
>>> +		}
>>> +
>>> +		/* Compute uncertainty in timestamp of scanout position query.
*/
>>> +		duration_ns = ktime_to_ns(etime) - ktime_to_ns(stime);
>>> +
>>> +		/* Accept result with <  max_error nsecs timing uncertainty.
*/
>>> +		if (duration_ns <= *max_error)
>>> +			break;
>>> +	}
>>> +
>>> +	/* Noisy system timing? */
>>> +	if (i == I915_TIMESTAMP_MAXRETRIES) {
>>> +		DRM_DEBUG("crtc %u: Noisy timestamp %d us > %d us [%d
reps].\n",
>>> +			  pipe, duration_ns/1000, *max_error/1000, i);
>>> +	}
>>> +
>>> +	/* Return upper bound of timestamp precision error. */
>>> +	*max_error = duration_ns;
>>> +
>>> +	/* Convert scanout position into elapsed time at raw_time query
>>> +	 * since start of scanout at first display scanline. delta_ns
>>> +	 * can be negative if start of scanout hasn't happened yet.
>>> +	 */
>>> +	delta_ns = div_s64(1000000LL * (vpos * mode->crtc_htotal +
hpos),
>>> +			   mode->crtc_clock);
>>> +
>>> +	/* Subtract time delta from raw timestamp to get final
>>> +	 * vblank_time timestamp for end of vblank.
>>> +	 */
>>> +	*vblank_time = ktime_sub_ns(etime, delta_ns);
>>> +
>>> +	if (!drm_debug_enabled(DRM_UT_VBL))
>>> +		return true;
>>> +
>>> +	ts_etime = ktime_to_timespec64(etime);
>>> +	ts_vblank_time = ktime_to_timespec64(*vblank_time);
>>> +
>>> +	DRM_DEBUG_VBL("crtc %u : v p(%d,%d)@ %lld.%06ld ->
%lld.%06ld [e %d us, %d rep]\n",
>>> +		      pipe, hpos, vpos,
>>> +		      (u64)ts_etime.tv_sec, ts_etime.tv_nsec / 1000,
>>> +		      (u64)ts_vblank_time.tv_sec, ts_vblank_time.tv_nsec / 1000,
>>> +		      duration_ns / 1000, i);
>>> +
>>> +	return true;
>>> +}
>>> +
>>>  int intel_get_crtc_scanline(struct intel_crtc *crtc)
>>>  {
>>>  	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
>>> diff --git a/drivers/gpu/drm/i915/i915_irq.h
b/drivers/gpu/drm/i915/i915_irq.h
>>> index 812c47a9c2d6..5f7b133ce721 100644
>>> --- a/drivers/gpu/drm/i915/i915_irq.h
>>> +++ b/drivers/gpu/drm/i915/i915_irq.h
>>> @@ -101,10 +101,11 @@ void gen8_irq_power_well_post_enable(struct
drm_i915_private *dev_priv,
>>>  void gen8_irq_power_well_pre_disable(struct drm_i915_private
*dev_priv,
>>>  				     u8 pipe_mask);
>>>  
>>> -bool i915_get_crtc_scanoutpos(struct drm_device *dev, unsigned int
pipe,
>>> -			      bool in_vblank_irq, int *vpos, int *hpos,
>>> -			      ktime_t *stime, ktime_t *etime,
>>> -			      const struct drm_display_mode *mode);
>>> +bool i915_calc_vbltimestamp_from_scanoutpos(struct drm_device
*dev,
>>> +					    unsigned int pipe,
>>> +					    int *max_error,
>>> +					    ktime_t *vblank_time,
>>> +					    bool in_vblank_irq);
>>>  
>>>  u32 i915_get_vblank_counter(struct drm_crtc *crtc);
>>>  u32 g4x_get_vblank_counter(struct drm_crtc *crtc);
>> 
-- 
Jani Nikula, Intel Open Source Graphics Center