Re: [PATCH] drm/msm/mdp5: enable autocommit

[Brian Masney <masneyb@onstation.org>]

Hi Jeffrey,

On Wed, Nov 13, 2019 at 06:23:34AM -0500, Brian Masney wrote:
> On Tue, Nov 12, 2019 at 08:38:27AM -0700, Jeffrey Hugo wrote:
> > On Tue, Nov 12, 2019 at 3:49 AM Brian Masney <masneyb@onstation.org> wrote:
> > >
> > > Since the introduction of commit 2d99ced787e3 ("drm/msm: async commit
> > > support"), command-mode panels began throwing the following errors:
> > >
> > >     msm fd900000.mdss: pp done time out, lm=0
> > >
> > > Let's fix this by enabling the autorefresh feature that's available in
> > > the MDP starting at version 1.0. This will cause the MDP to
> > > automatically send a frame to the panel every time the panel invokes
> > > the TE signal, which will trigger the PP_DONE IRQ. This requires not
> > > sending a START signal for command-mode panels.
> > >
> > > This fixes the error and gives us a counter for command-mode panels that
> > > we can use to implement async commit support for the MDP5 in a follow up
> > > patch.
> > >
> > > Signed-off-by: Brian Masney <masneyb@onstation.org>
> > > Suggested-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>
> > > ---
> > >  drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c | 15 ++++++++++++++-
> > >  drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c  |  9 +--------
> > >  2 files changed, 15 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c
> > > index 05cc04f729d6..539348cb6331 100644
> > > --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c
> > > +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_crtc.c
> > > @@ -456,6 +456,7 @@ static void mdp5_crtc_atomic_enable(struct drm_crtc *crtc,
> > >  {
> > >         struct mdp5_crtc *mdp5_crtc = to_mdp5_crtc(crtc);
> > >         struct mdp5_crtc_state *mdp5_cstate = to_mdp5_crtc_state(crtc->state);
> > > +       struct mdp5_pipeline *pipeline = &mdp5_cstate->pipeline;
> > >         struct mdp5_kms *mdp5_kms = get_kms(crtc);
> > >         struct device *dev = &mdp5_kms->pdev->dev;
> > >
> > > @@ -493,9 +494,21 @@ static void mdp5_crtc_atomic_enable(struct drm_crtc *crtc,
> > >
> > >         mdp_irq_register(&mdp5_kms->base, &mdp5_crtc->err);
> > >
> > > -       if (mdp5_cstate->cmd_mode)
> > > +       if (mdp5_cstate->cmd_mode) {
> > >                 mdp_irq_register(&mdp5_kms->base, &mdp5_crtc->pp_done);
> > >
> > > +               /*
> > > +                * Enable autorefresh so we get regular ping/pong IRQs.
> > > +                * - Bit 31 is the enable bit
> > > +                * - Bits 0-15 represent the frame count, specifically how many
> > > +                *   TE events before the MDP sends a frame.
> > > +                */
> > > +               mdp5_write(mdp5_kms,
> > > +                          REG_MDP5_PP_AUTOREFRESH_CONFIG(pipeline->mixer->pp),
> > > +                          BIT(31) | BIT(0));
> > > +               crtc_flush_all(crtc);
> > > +       }
> > > +
> > >         mdp5_crtc->enabled = true;
> > >  }
> > >
> > > diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c
> > > index 030279d7b64b..aee295abada3 100644
> > > --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c
> > > +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c
> > > @@ -187,14 +187,7 @@ static bool start_signal_needed(struct mdp5_ctl *ctl,
> > >         if (!ctl->encoder_enabled)
> > >                 return false;
> > >
> > > -       switch (intf->type) {
> > > -       case INTF_WB:
> > > -               return true;
> > > -       case INTF_DSI:
> > > -               return intf->mode == MDP5_INTF_DSI_MODE_COMMAND;
> > > -       default:
> > > -               return false;
> > > -       }
> > > +       return intf->type == INTF_WB;
> > >  }
> > 
> > I don't think this fully works.
> > 
> > The whole "flush" thing exists because the configuration is double
> > buffered.  You write to the flush register to tell the hardware to
> > pickup the new configuration, but it doesn't do that automatically.
> > It only picks up the new config on the next "vsync".  When you have a
> > video mode panel, you have the timing engine running, which drives
> > that.  With a command mode panel, you have either the start signal, or
> > the auto refresh to do the same, but you have a bit of a chicken and
> > egg situation where if you are programming the hardware from scratch,
> > autorefresh isn't already enabled to then pickup the config to enable
> > autorefresh. In this case, you'll need a single start to kick
> > everything off.  However, if say the bootloader already configured
> > things and has autorefresh running, then you need to not do that start
> > because you'll overload the DSI like you saw.
> 
> As part of my testing for this work, I added a log statement to
> mdp5_crtc_pp_done_irq() and it shows that a PP_IRQ comes in consistently
> every ~0.0166 seconds, which is about 60 HZ. Without this change, plus
> the 3 commits I mentioned in an earlier email related to the async
> commit support, the PP IRQs come in at a variety of times: between every
> ~0.0140 and ~0.2224 seconds. That's why I assumed that this was working.
> 
> If I call send_start_signal() inside mdp5_crtc_atomic_enable(), then the
> display does not work properly.

I'd like to get the 'pp done time out' errors that are now occurring
upstream for command-mode panels fixed. As I mentioned above, this patch
fixes the problem on the Nexus 5 and the pp done interrupts are
delivered at approximately 60 HZ. I don't have any other command-mode
panels to test.

I'm not sure how to proceed here since sending the start command breaks
the display. I'm likely putting that command in the wrong spot.

Brian