linux-kernel - Re: [PATCH 3/6] clk: meson: meson8b: Add the HDMI PLL M/N parameters

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Message-ID: <1jfstvschd.fsf@starbuckisacylon.baylibre.com>
Date:   Thu, 23 Sep 2021 14:22:37 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        linux-amlogic@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-clk@...r.kernel.org, narmstrong@...libre.com
Subject: Re: [PATCH 3/6] clk: meson: meson8b: Add the HDMI PLL M/N parameters


On Wed 14 Jul 2021 at 01:25, Martin Blumenstingl <martin.blumenstingl@...glemail.com> wrote:

> The 3.10 vendor kernel uses only specific HDMI PLL M/N parameter
> combinations. The PLL won't lock for values smaller than 50 if the
> internal doubling (which is yet unknown how to use it) is disabled.
> However, when this doubling is enabled then the values smaller than 50
> will lock just fine. The only restriction for values greater than 50 is
> that the resulting frequency must not exceed the 3.0GHz limit.

Hum, it's not the first time we have that type of issue.
I'm thinking that, instead of using mult_range, we should probably have
min and max output frequencies . The datasheet usually documents these
values for PLL DCO. Something to think about ...

>
> These values are taken from the endlessm 3.10 kernel which includes
> additional M/N combinations for some VESA and 75Hz display modes.
>
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
> ---
>  drivers/clk/meson/meson8b.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>
> diff --git a/drivers/clk/meson/meson8b.c b/drivers/clk/meson/meson8b.c
> index 9ccffbfe44e5..8f29d26ed726 100644
> --- a/drivers/clk/meson/meson8b.c
> +++ b/drivers/clk/meson/meson8b.c
> @@ -118,6 +118,27 @@ static struct clk_regmap meson8b_fixed_pll = {
>  	},
>  };
>  
> +static const struct pll_params_table hdmi_pll_params_table[] = {
> +	PLL_PARAMS(40, 1),
> +	PLL_PARAMS(42, 1),
> +	PLL_PARAMS(44, 1),
> +	PLL_PARAMS(45, 1),
> +	PLL_PARAMS(49, 1),
> +	PLL_PARAMS(52, 1),
> +	PLL_PARAMS(54, 1),
> +	PLL_PARAMS(56, 1),
> +	PLL_PARAMS(59, 1),
> +	PLL_PARAMS(60, 1),
> +	PLL_PARAMS(61, 1),
> +	PLL_PARAMS(62, 1),
> +	PLL_PARAMS(64, 1),
> +	PLL_PARAMS(66, 1),
> +	PLL_PARAMS(68, 1),
> +	PLL_PARAMS(71, 1),
> +	PLL_PARAMS(82, 1),
> +	{ /* sentinel */ }
> +};
> +
>  static struct clk_regmap meson8b_hdmi_pll_dco = {
>  	.data = &(struct meson_clk_pll_data){
>  		.en = {
> @@ -150,6 +171,7 @@ static struct clk_regmap meson8b_hdmi_pll_dco = {
>  			.shift   = 29,
>  			.width   = 1,
>  		},
> +		.table = hdmi_pll_params_table,
>  	},
>  	.hw.init = &(struct clk_init_data){
>  		/* sometimes also called "HPLL" or "HPLL PLL" */