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

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Date:   Fri, 18 Dec 2020 11:37:50 +0000
From:   Dave Stevenson <dave.stevenson@...pberrypi.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Eric Anholt <eric@...olt.net>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Jason Cooper <jason@...edaemon.net>,
        bcm-kernel-feedback-list@...adcom.com,
        linux-arm-kernel@...ts.infradead.org,
        Marc Zyngier <maz@...nel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        LKML <linux-kernel@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-rpi-kernel@...ts.infradead.org,
        DRI Development <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 08/15] drm/vc4: hdmi: Introduce a CEC clock

Hi Maxime

On Thu, 10 Dec 2020 at 13:47, Maxime Ripard <maxime@...no.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@...no.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?

Otherwise I'm happy with the patch.

  Dave

> +
>         vc4_hdmi->reset = devm_reset_control_get(dev, NULL);
>         if (IS_ERR(vc4_hdmi->reset)) {
>                 DRM_ERROR("Failed to get HDMI reset line\n");
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.h b/drivers/gpu/drm/vc4/vc4_hdmi.h
> index 720914761261..adc4bf33ff15 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.h
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.h
> @@ -155,6 +155,7 @@ struct vc4_hdmi {
>         bool cec_tx_ok;
>         bool cec_irq_was_rx;
>
> +       struct clk *cec_clock;
>         struct clk *pixel_clock;
>         struct clk *hsm_clock;
>         struct clk *audio_clock;
> --
> 2.28.0
>