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Date:   Fri, 18 Dec 2020 13:23:34 +0100
From:   Maxime Ripard <maxime@cerno.tech>
To:     Dave Stevenson <dave.stevenson@raspberrypi.com>
Cc:     Eric Anholt <eric@anholt.net>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Daniel Vetter <daniel.vetter@intel.com>,
        David Airlie <airlied@linux.ie>,
        Jason Cooper <jason@lakedaemon.net>,
        bcm-kernel-feedback-list@broadcom.com,
        linux-arm-kernel@lists.infradead.org,
        Marc Zyngier <maz@kernel.org>,
        Linux Media Mailing List <linux-media@vger.kernel.org>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        LKML <linux-kernel@vger.kernel.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-rpi-kernel@lists.infradead.org,
        DRI Development <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH 08/15] drm/vc4: hdmi: Introduce a CEC clock
Message-ID: <20201218122334.tvdeslyyuus4hp4y@gilmour>
References: <20201210134648.272857-1-maxime@cerno.tech>
 <20201210134648.272857-9-maxime@cerno.tech>
 <CAPY8ntA7dS1Ew+mF=xRdWFF0P071=O5X7vVKt7O_iiTdUbJM5g@mail.gmail.com>
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Hi Dave,

On Fri, Dec 18, 2020 at 11:37:50AM +0000, Dave Stevenson wrote:
> Hi Maxime
>=20
> On Thu, 10 Dec 2020 at 13:47, Maxime Ripard <maxime@cerno.tech> 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@cerno.tech>
> > ---
> >  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_h=
dmi.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 =3D clk_get_rate(vc4_hdmi->hsm_clock) / CEC_CLOCK_FREQ;
> > +       clk_cnt =3D clk_get_rate(vc4_hdmi->cec_clock) / CEC_CLOCK_FREQ;
> >         value |=3D 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_hdm=
i *vc4_hdmi)
> >                 return PTR_ERR(vc4_hdmi->hsm_clock);
> >         }
> >         vc4_hdmi->audio_clock =3D vc4_hdmi->hsm_clock;
> > +       vc4_hdmi->cec_clock =3D vc4_hdmi->hsm_clock;
> >
> >         return 0;
> >  }
> > @@ -1833,6 +1834,12 @@ static int vc5_hdmi_init_resources(struct vc4_hd=
mi *vc4_hdmi)
> >                 return PTR_ERR(vc4_hdmi->audio_clock);
> >         }
> >
> > +       vc4_hdmi->cec_clock =3D 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);
> > +       }
>=20
> Aren't we adding to the DT binding here and breaking backwards compatibil=
ity?
> 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=3D2e3725b05b785e73482a194b99bff3d5a1c85140

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

Maxime

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