Re: [PATCH 1/2] drm/mxsfb: Call drm_crtc_vblank_on/off

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, May 28, 2020 at 10:19:46AM +0200, Stefan Agner wrote:
> On 2020-05-28 10:06, Daniel Vetter wrote:
> > On Thu, May 28, 2020 at 9:56 AM Stefan Agner <stefan@agner.ch> wrote:
> >>
> >> Hi Daniel,
> >>
> >> On 2020-05-28 07:46, Daniel Vetter wrote:
> >> > On Wed, May 27, 2020 at 11:47:56AM +0200, Daniel Vetter wrote:
> >> >> mxsfb has vblank support, is atomic, but doesn't call
> >> >> drm_crtc_vblank_on/off as it should. Not good.
> >> >>
> >> >> With my next patch to add the drm_crtc_vblank_reset to helpers this
> >> >> means not even the very first crtc enabling will vblanks work anymore,
> >> >> since they'll just stay off forever.
> >> >>
> >> >> Since mxsfb doesn't have any vblank waits of its own in the
> >> >> enable/disable flow, nor an enable/disable_vblank callback we can do
> >> >> the on/off as the first respectively last operation, and it should all
> >> >> work.
> >> >>
> >> >> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> >> >> Cc: Marek Vasut <marex@denx.de>
> >> >> Cc: Stefan Agner <stefan@agner.ch>
> >> >> Cc: Shawn Guo <shawnguo@kernel.org>
> >> >> Cc: Sascha Hauer <s.hauer@pengutronix.de>
> >> >> Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
> >> >> Cc: Fabio Estevam <festevam@gmail.com>
> >> >> Cc: NXP Linux Team <linux-imx@nxp.com>
> >> >> Cc: linux-arm-kernel@lists.infradead.org
> >> >
> >> > Ping for some ack/review on this one here, it's holding up the subsystem
> >> > wide fix in patch 2.
> >>
> >> Sorry for the delay.
> >>
> >> I guess that has the same effect as patch 14 in Laurent's patchset would
> >> have:
> >> https://lore.kernel.org/dri-devel/20200309195216.31042-15-laurent.pinchart@ideasonboard.com/
> > 
> > Uh, looking at that patch I realized that mxsfb indeed calls
> > drm_vblank_init before mode_config.num_crtc is set. Which means it
> > never had working vblank support in upstream. That also explains the
> > lack of fireworks, since all other drivers that actually do initialize
> > vblank support have the drm_crtc_vblank_on/off calls - without them
> > the driver doesn't survive for very long.
> > 
> > tldr; I don't need this patch here to apply the 2nd one, so no
> > conflict potential at all. And the patch from Laurent does fix up
> > everything correctly, so we should be good.
> 
> Uh I see, that is somehow unfortunate and fortunate at the same time!
> 
> Ok, I hope we get this cleaned up soon.

I recommend igt tests for actually making sure your driver does something,
instead of just thinking you've enabled a feature :-)
-Daniel

> 
> --
> Stefan
> 
> > -Daniel
> > 
> >> But should be rather trivial to rebase. So until Laurent's patchset is
> >> ready, we can go with this fix.
> >>
> >> Acked-by: Stefan Agner <stefan@agner.ch>
> >>
> >> --
> >> Stefan
> >>
> >> >
> >> > Thanks, Daniel
> >> >
> >> >> ---
> >> >>  drivers/gpu/drm/mxsfb/mxsfb_drv.c | 2 ++
> >> >>  1 file changed, 2 insertions(+)
> >> >>
> >> >> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.c b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> >> >> index 497cf443a9af..1891cd6deb2f 100644
> >> >> --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> >> >> +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> >> >> @@ -124,6 +124,7 @@ static void mxsfb_pipe_enable(struct drm_simple_display_pipe *pipe,
> >> >>      drm_panel_prepare(mxsfb->panel);
> >> >>      mxsfb_crtc_enable(mxsfb);
> >> >>      drm_panel_enable(mxsfb->panel);
> >> >> +    drm_crtc_vblank_on(&pipe->crtc);
> >> >>  }
> >> >>
> >> >>  static void mxsfb_pipe_disable(struct drm_simple_display_pipe *pipe)
> >> >> @@ -133,6 +134,7 @@ static void mxsfb_pipe_disable(struct drm_simple_display_pipe *pipe)
> >> >>      struct drm_crtc *crtc = &pipe->crtc;
> >> >>      struct drm_pending_vblank_event *event;
> >> >>
> >> >> +    drm_crtc_vblank_off(&pipe->crtc);
> >> >>      drm_panel_disable(mxsfb->panel);
> >> >>      mxsfb_crtc_disable(mxsfb);
> >> >>      drm_panel_unprepare(mxsfb->panel);
> >> >> --
> >> >> 2.26.2
> >> >>

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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