From: Daniel Vetter <daniel@ffwll.ch>
To: Robert Beckett <bob.beckett@collabora.com>
Cc: Fabio Estevam <festevam@gmail.com>,
Philipp Zabel <p.zabel@pengutronix.de>,
Maxime Ripard <maxime.ripard@bootlin.com>,
Shawn Guo <shawnguo@kernel.org>,
Sascha Hauer <s.hauer@pengutronix.de>,
Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
David Airlie <airlied@linux.ie>,
NXP Linux Team <linux-imx@nxp.com>,
Daniel Vetter <daniel@ffwll.ch>, Sean Paul <sean@poorly.run>,
Pengutronix Kernel Team <kernel@pengutronix.de>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 1/4] drm/vblank: warn on sending stale event
Date: Tue, 25 Jun 2019 22:00:42 +0200 [thread overview]
Message-ID: <20190625200042.GC12905@phenom.ffwll.local> (raw)
In-Reply-To: <a21034afa30246f31daa16e74a0772377a4791ef.1561483965.git.bob.beckett@collabora.com>
On Tue, Jun 25, 2019 at 06:59:12PM +0100, Robert Beckett wrote:
> Warn when about to send stale vblank info and add advice to
> documentation on how to avoid.
>
> Signed-off-by: Robert Beckett <bob.beckett@collabora.com>
> ---
> drivers/gpu/drm/drm_vblank.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 603ab105125d..7dabb2bdb733 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -918,6 +918,19 @@ EXPORT_SYMBOL(drm_crtc_arm_vblank_event);
> *
> * See drm_crtc_arm_vblank_event() for a helper which can be used in certain
> * situation, especially to send out events for atomic commit operations.
> + *
> + * Care should be taken to avoid stale timestamps. If:
> + * - your driver has vblank support (i.e. dev->num_crtcs > 0)
> + * - the vblank irq is off (i.e. no one called drm_crtc_vblank_get)
drm_crtc_vblank_get() so it becomes a neat hyperlink.
> + * - from the vblank code's pov the pipe is still running (i.e. not
> + * in-between a drm_crtc_vblank_off()/on() pair)
Not sure the above will lead to great markup, maybe spell out the
drm_crtc_vblank_on() and maybe make it a bit clearer like "i.e. not after
the call to drm_crtc_vblank_off() but before the next call to
drm_crtc_vblank_on()" so it's clear which said of this pair we're talking
about.
> + * If all of these conditions hold then drm_crtc_send_vblank_event is
style nit: the enumeration is one sentence (and and oxford comman missing
but whatever), but you don't continue it here. Also, does the enumeration
look pretty in the htmldocs output?
> + * going to give you a garbage timestamp and and sequence number (the last
> + * recorded before the irq was disabled). If you call drm_crtc_vblank_get/put
> + * around it, or after vblank_off, then either of those will have rolled things
> + * forward for you.
Again pls fix the markup so all the function reference stick out and work.
> + * So, drivers should call drm_crtc_vblank_off() before this function in their
> + * crtc atomic_disable handlers.
Imo this sentence here is needed but a bit confusing, and we have it
documented already in the atomic_disable hook.
Other option would be to list all the places where a driver might want to
call this and how they could get it wrong, which imo doesn't make sense.
With the nits addressed:
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> */
> void drm_crtc_send_vblank_event(struct drm_crtc *crtc,
> struct drm_pending_vblank_event *e)
> @@ -925,8 +938,12 @@ void drm_crtc_send_vblank_event(struct drm_crtc *crtc,
> struct drm_device *dev = crtc->dev;
> u64 seq;
> unsigned int pipe = drm_crtc_index(crtc);
> + struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> ktime_t now;
>
> + WARN_ONCE(dev->num_crtcs > 0 && !vblank->enabled && !vblank->inmodeset,
> + "sending stale vblank info\n");
> +
> if (dev->num_crtcs > 0) {
> seq = drm_vblank_count_and_time(dev, pipe, &now);
> } else {
> --
> 2.18.0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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next prev parent reply other threads:[~2019-06-25 20:01 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-25 17:59 [PATCH v3 0/4] handle vblank when disabling ctc with interrupt disabled (was [PATCH v2] drm/imx: correct order of crtc disable) Robert Beckett
2019-06-25 17:59 ` [PATCH v3 1/4] drm/vblank: warn on sending stale event Robert Beckett
2019-06-25 20:00 ` Daniel Vetter [this message]
2019-06-25 20:02 ` Daniel Vetter
2019-06-25 17:59 ` [PATCH v3 2/4] drm/imx: notify drm core before sending event during crtc disable Robert Beckett
2019-06-25 20:03 ` Daniel Vetter
2019-06-25 17:59 ` [PATCH v3 3/4] drm/vblank: estimate vblank while disabling vblank if interrupt disabled Robert Beckett
2019-06-25 20:11 ` Daniel Vetter
2019-06-26 13:27 ` Ville Syrjälä
2019-06-26 14:30 ` Daniel Vetter
2019-06-25 17:59 ` [PATCH v3 4/4] drm/imx: only send event on crtc disable if kept disabled Robert Beckett
2019-06-25 20:22 ` Daniel Vetter
2019-06-26 8:33 ` Philipp Zabel
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