Re: [PATCH v3 3/4] drm/vblank: estimate vblank while disabling vblank if interrupt disabled

Ville Syrjälä
2019-06-26T13:27:42Z

On Tue, Jun 25, 2019 at 06:59:14PM +0100, Robert Beckett wrote:
> If interrupts are disabled (e.g. via vblank_disable_fn) and we come to
> disable vblank, update the vblank count to best guess as to what it
> would be had the interrupts remained enabled, and update the timesamp to
> now.
>
> This avoids a stale vblank event being sent while disabling crtcs during
> atomic modeset.
>
> Fixes: 68036b08b91bc ("drm/vblank: Do not update vblank count if interrupts
> are already disabled.")

I don't understand that commit. drm_vblank_off() should be called
when the power is still present, so it looks to me like that
commit is actually wrong. So I think we may want to just revert
it and figure out what the actual bug was.

>
> Signed-off-by: Robert Beckett <bob.beckett@collabora.com>
> ---
> drivers/gpu/drm/drm_vblank.c | 16 +++++++++++++++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 7dabb2bdb733..db68b8cbf797 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -375,9 +375,23 @@ void drm_vblank_disable_and_save(struct drm_device *dev, unsigned int pipe)
> * interrupts were enabled. This avoids calling the ->disable_vblank()
> * operation in atomic context with the hardware potentially runtime
> * suspended.
> + * If interrupts are disabled (e.g. via blank_disable_fn) then make
> + * best guess as to what it would be now and make sure we have an up
> + * to date timestamp.
> */
> - if (!vblank->enabled)
> + if (!vblank->enabled) {
> + ktime_t now = ktime_get();
> + u32 diff = 0;
> + if (vblank->framedur_ns) {
> + u64 diff_ns = ktime_to_ns(ktime_sub(now, vblank->time));
> + diff = DIV_ROUND_CLOSEST_ULL(diff_ns,
> + vblank->framedur_ns);
> + }
> +
> + store_vblank(dev, pipe, diff, now, vblank->count);
> +
> goto out;
> + }
>
> /*
> * Update the count and timestamp to maintain the
> --
> 2.18.0
>
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--
Ville Syrjälä
Intel