On Mon, Apr 11, 2016 at 11:42:57AM +0200, Maarten Lankhorst wrote:
> This function is useful for gen2 intel devices which have no frame
> counter, but need a way to determine the current vblank count without
> racing with the vblank interrupt handler.
>
> intel_pipe_update_start checks if no vblank interrupt will occur
> during vblank evasion, but cannot check whether the vblank handler has
> run to completion. This function uses the timestamps to determine
> when the last vblank has happened, and interpolates from there.
>
> Changes since v1:
> - Take vblank_time_lock and don't use drm_vblank_count_and_time.
>
> Cc: Mario Kleiner <mario.kleiner.de@xxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_irq.c | 31 +++++++++++++++++++++++++++++++
> include/drm/drmP.h | 2 ++
> 2 files changed, 33 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index 3c1a6f18e71c..d3cecc1932e1 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -303,6 +303,37 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> store_vblank(dev, pipe, diff, &t_vblank, cur_vblank);
> }
>
> +/**
> + * drm_accurate_vblank_count_and_time - retrieve the master vblank counter
> + * @crtc: which counter to retrieve
> + * @tv_ret: last time counter was updated
> + *
> + * This function is similar to @drm_update_vblank_count_and_time but
> + * this function interpolates to handle a race with vblank irq's, and
> + * is only useful for crtc's that have no hw vblank counter.
> + */
> +
> +u32 drm_accurate_vblank_count_and_time(struct drm_crtc *crtc,
> + struct timeval *tv_ret)
> +{
> + struct drm_device *dev = crtc->dev;
> + u32 vblank, pipe = drm_crtc_index(crtc);
> + unsigned long flags;
> +
> + WARN(dev->max_vblank_count, "This function is only useful when a hw counter is unavailable.");
It's useful on everything if you actually want to trust the
software counter to not be stale.
> +
> + spin_lock_irqsave(&dev->vblank_time_lock, flags);
> + drm_update_vblank_count(dev, pipe, 0);
> +
> + vblank = dev->vblank[pipe].count;
> + *tv_ret = vblanktimestamp(dev, pipe, vblank);
Do we have a user in mind that would care about the timestamp?
> +
> + spin_unlock_irqrestore(&dev->vblank_time_lock, flags);
> +
> + return vblank;
> +}
> +EXPORT_SYMBOL(drm_accurate_vblank_count_and_time);
> +
> /*
> * Disable vblank irq's on crtc, make sure that last vblank count
> * of hardware and corresponding consistent software vblank counter
> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> index 31483c2fef51..1df65922c7c6 100644
> --- a/include/drm/drmP.h
> +++ b/include/drm/drmP.h
> @@ -995,6 +995,8 @@ extern void drm_crtc_vblank_off(struct drm_crtc *crtc);
> extern void drm_crtc_vblank_reset(struct drm_crtc *crtc);
> extern void drm_crtc_vblank_on(struct drm_crtc *crtc);
> extern void drm_vblank_cleanup(struct drm_device *dev);
> +extern u32 drm_accurate_vblank_count_and_time(struct drm_crtc *crtc,
> + struct timeval *tv_ret);
> extern u32 drm_vblank_no_hw_counter(struct drm_device *dev, unsigned int pipe);
>
> extern int drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
> --
> 2.1.0
>
--
Ville Syrjälä
Intel OTC
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