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

From: Dave Stevenson <dave.stevenson@raspberrypi.com>
To: Maxime Ripard <maxime@cerno.tech>
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
Date: Fri, 18 Dec 2020 12:25:00 +0000	[thread overview]
Message-ID: <CAPY8ntDwp5+8+uB3xVR=mVTZYPLXp1CiYe5AFFium1JQaQNZNw@mail.gmail.com> (raw)
In-Reply-To: <20201218122334.tvdeslyyuus4hp4y@gilmour>

On Fri, 18 Dec 2020 at 12:23, Maxime Ripard <maxime@cerno.tech> wrote:
>
> 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@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_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

I guess I should have read it then :-)
In which case
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>