On Tue, Mar 29, 2016 at 03:38:55PM +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.
Didn't really read it in detail, but on a glance it seems too
complicated to me. All we should really need is something like this:
drm_vblank_get();
drm_update_vblank_count();
accurate = drm_vblank_count();
>
> Cc: Mario Kleiner <mario.kleiner.de@xxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> ---
> Unfortunately only compile time tested, I don't have a gen2 to test with.
>
> drivers/gpu/drm/drm_irq.c | 90 +++++++++++++++++++++++++++++++++++------------
> include/drm/drmP.h | 2 ++
> 2 files changed, 69 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index 881c5a6c180c..44d8f9607ccd 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -155,24 +155,10 @@ static void drm_reset_vblank_timestamp(struct drm_device *dev, unsigned int pipe
> spin_unlock(&dev->vblank_time_lock);
> }
>
> -/**
> - * drm_update_vblank_count - update the master vblank counter
> - * @dev: DRM device
> - * @pipe: counter to update
> - *
> - * Call back into the driver to update the appropriate vblank counter
> - * (specified by @pipe). Deal with wraparound, if it occurred, and
> - * update the last read value so we can deal with wraparound on the next
> - * call if necessary.
> - *
> - * Only necessary when going from off->on, to account for frames we
> - * didn't get an interrupt for.
> - *
> - * Note: caller must hold dev->vbl_lock since this reads & writes
> - * device vblank fields.
> - */
> -static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> - unsigned long flags)
> +static u32 __drm_accurate_vblank_count_and_time(struct drm_device *dev, unsigned int pipe,
> + const struct timeval *t_old,
> + unsigned long flags, u32 *pdiff,
> + struct timeval *tv_ret)
> {
> struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> u32 cur_vblank, diff;
> @@ -202,10 +188,8 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> /* trust the hw counter when it's around */
> diff = (cur_vblank - vblank->last) & dev->max_vblank_count;
> } else if (rc && framedur_ns) {
> - const struct timeval *t_old;
> u64 diff_ns;
>
> - t_old = &vblanktimestamp(dev, pipe, vblank->count);
> diff_ns = timeval_to_ns(&t_vblank) - timeval_to_ns(t_old);
>
> /*
> @@ -286,9 +270,13 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> " current=%u, diff=%u, hw=%u hw_last=%u\n",
> pipe, vblank->count, diff, cur_vblank, vblank->last);
>
> + *pdiff = diff;
> + *tv_ret = t_vblank;
> +
> if (diff == 0) {
> WARN_ON_ONCE(cur_vblank != vblank->last);
> - return;
> +
> + return cur_vblank;
> }
>
> /*
> @@ -298,9 +286,65 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> * for now, to mark the vblanktimestamp as invalid.
> */
> if (!rc && (flags & DRM_CALLED_FROM_VBLIRQ) == 0)
> - t_vblank = (struct timeval) {0, 0};
> + *tv_ret = (struct timeval) {0, 0};
> +
> + return 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 pdiff, old_vblank;
> + struct timeval tv_old = {};
> +
> + WARN(dev->max_vblank_count, "This function is only useful when a hw counter is unavailable.");
> +
> + old_vblank = drm_crtc_vblank_count_and_time(crtc, &tv_old);
> +
> + __drm_accurate_vblank_count_and_time(dev, drm_crtc_index(crtc),
> + &tv_old, 0, &pdiff, tv_ret);
> +
> + return old_vblank + pdiff;
> +}
> +EXPORT_SYMBOL(drm_accurate_vblank_count_and_time);
> +
> +/**
> + * drm_update_vblank_count - update the master vblank counter
> + * @dev: DRM device
> + * @pipe: counter to update
> + *
> + * Call back into the driver to update the appropriate vblank counter
> + * (specified by @pipe). Deal with wraparound, if it occurred, and
> + * update the last read value so we can deal with wraparound on the next
> + * call if necessary.
> + *
> + * Only necessary when going from off->on, to account for frames we
> + * didn't get an interrupt for.
> + *
> + * Note: caller must hold dev->vbl_lock since this reads & writes
> + * device vblank fields.
> + */
> +static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> + unsigned long flags)
> +{
> + u32 diff, cur_vblank, old_vblank = dev->vblank[pipe].count;
> + struct timeval t_vblank;
> + const struct timeval *tv_old = &vblanktimestamp(dev, pipe, old_vblank);
>
> - store_vblank(dev, pipe, diff, &t_vblank, cur_vblank);
> + cur_vblank = __drm_accurate_vblank_count_and_time(dev, pipe, tv_old, flags, &diff, &t_vblank);
> + if (diff)
> + store_vblank(dev, pipe, diff, &t_vblank, cur_vblank);
> }
>
> /*
> 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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