Re: [PATCH 08/15] drm/vc4: hdmi: Introduce a CEC clock

[Maxime Ripard]

Hi Dave,

On Fri, Dec 18, 2020 at 11:37:50AM +0000, Dave Stevenson wrote:
> Hi Maxime
> 
> On Thu, 10 Dec 2020 at 13:47, Maxime Ripard <maxime@xxxxxxxxxx> wrote:
> >
> > While the BCM2835 had the CEC clock derived from the HSM clock, the
> > BCM2711 has a dedicated parent clock for it.
> >
> > Let's introduce a separate clock for it so that we can handle both
> > cases.
> >
> > Signed-off-by: Maxime Ripard <maxime@xxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/vc4/vc4_hdmi.c | 9 ++++++++-
> >  drivers/gpu/drm/vc4/vc4_hdmi.h | 1 +
> >  2 files changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > index b93ee3e26e2b..0debd22bc992 100644
> > --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> > +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > @@ -145,7 +145,7 @@ static void vc4_hdmi_cec_update_clk_div(struct vc4_hdmi *vc4_hdmi)
> >          * Set the clock divider: the hsm_clock rate and this divider
> >          * setting will give a 40 kHz CEC clock.
> >          */
> > -       clk_cnt = clk_get_rate(vc4_hdmi->hsm_clock) / CEC_CLOCK_FREQ;
> > +       clk_cnt = clk_get_rate(vc4_hdmi->cec_clock) / CEC_CLOCK_FREQ;
> >         value |= clk_cnt << VC4_HDMI_CEC_DIV_CLK_CNT_SHIFT;
> >         HDMI_WRITE(HDMI_CEC_CNTRL_1, value);
> >  }
> > @@ -1740,6 +1740,7 @@ static int vc4_hdmi_init_resources(struct vc4_hdmi *vc4_hdmi)
> >                 return PTR_ERR(vc4_hdmi->hsm_clock);
> >         }
> >         vc4_hdmi->audio_clock = vc4_hdmi->hsm_clock;
> > +       vc4_hdmi->cec_clock = vc4_hdmi->hsm_clock;
> >
> >         return 0;
> >  }
> > @@ -1833,6 +1834,12 @@ static int vc5_hdmi_init_resources(struct vc4_hdmi *vc4_hdmi)
> >                 return PTR_ERR(vc4_hdmi->audio_clock);
> >         }
> >
> > +       vc4_hdmi->cec_clock = devm_clk_get(dev, "cec");
> > +       if (IS_ERR(vc4_hdmi->cec_clock)) {
> > +               DRM_ERROR("Failed to get CEC clock\n");
> > +               return PTR_ERR(vc4_hdmi->cec_clock);
> > +       }
> 
> Aren't we adding to the DT binding here and breaking backwards compatibility?
> Admittedly CEC didn't work before (and was masked out) for vc5, but do
> we need to worry about those with existing DT files that currently
> work happily?

The DT compatibility is not a worry here: I made sure the CEC clock and
range were part of the binding since it's been introduced:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2e3725b05b785e73482a194b99bff3d5a1c85140

So we were not using it so far, but it was in the DT all along

Maxime

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