Re: [PATCH 03/23] drm/i915: Don't use struct drm_driver.get_scanout_position()

[Jani Nikula <jani.nikula@linux.intel.com>]

On Fri, 10 Jan 2020, Thomas Zimmermann <tzimmermann@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@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