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From:   Dave Stevenson <dave.stevenson@raspberrypi.com>
Date:   Tue, 28 Jul 2020 15:57:22 +0100
Message-ID: <CAPY8ntCkuN-cahLd7Ex4awkcUhFVM43nGX4rZCtjRmy-wCyHGQ@mail.gmail.com>
Subject: Re: [PATCH v4 63/78] drm/vc4: hdmi: Use clk_set_min_rate instead
To:     Maxime Ripard <maxime@cerno.tech>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        Eric Anholt <eric@anholt.net>,
        DRI Development <dri-devel@lists.freedesktop.org>,
        linux-rpi-kernel@lists.infradead.org,
        bcm-kernel-feedback-list@broadcom.com,
        linux-arm-kernel@lists.infradead.org,
        LKML <linux-kernel@vger.kernel.org>,
        Tim Gover <tim.gover@raspberrypi.com>,
        Phil Elwell <phil@raspberrypi.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi Maxime

On Wed, 8 Jul 2020 at 18:44, Maxime Ripard <maxime@cerno.tech> wrote:
>
> The HSM clock needs to be running at 101% the pixel clock of the HDMI
> controller, however it's shared between the two HDMI controllers, which
> means that if the resolutions are different between the two HDMI
> controllers, and the lowest resolution is on the second (in enable order)
> controller, the first HDMI controller will end up with a smaller than
> expected clock rate.
>
> Since we don't really need an exact frequency there, we can simply change
> the minimum rate we expect instead.
>
> Signed-off-by: Maxime Ripard <maxime@cerno.tech>

Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>

> ---
>  drivers/gpu/drm/vc4/vc4_hdmi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index 9f30fab744f2..d99188c90ff9 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -462,7 +462,7 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
>          * pixel clock, but HSM ends up being the limiting factor.
>          */
>         hsm_rate = max_t(unsigned long, 120000000, (pixel_rate / 100) * 101);
> -       ret = clk_set_rate(vc4_hdmi->hsm_clock, hsm_rate);
> +       ret = clk_set_min_rate(vc4_hdmi->hsm_clock, hsm_rate);
>         if (ret) {
>                 DRM_ERROR("Failed to set HSM clock rate: %d\n", ret);
>                 return;
> --
> git-series 0.9.1