linux-kernel - Re: [PATCH v4 02/13] clk: sunxi: add ahb1 clock for A83T

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Date:	Thu, 17 Mar 2016 11:40:42 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Vishnu Patekar <vishnupatekar0510@...il.com>
Cc:	robh+dt@...nel.org, corbet@....net, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, linux@....linux.org.uk, emilio@...pez.com.ar,
	jenskuske@...il.com, hdegoede@...hat.com, wens@...e.org,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com,
	linux-gpio@...r.kernel.org, linus.walleij@...aro.org,
	mturquette@...libre.com, sboyd@...eaurora.org,
	patchesrdh@...as.com, linux-clk@...r.kernel.org
Subject: Re: [PATCH v4 02/13] clk: sunxi: add ahb1 clock for A83T

On Thu, Mar 17, 2016 at 12:04:25AM +0800, Vishnu Patekar wrote:
> AHB1 on A83T is similar to ahb1 on A31, except parents are different.
> clock index 0b1x is PLL6.
> 
> Signed-off-by: Vishnu Patekar <vishnupatekar0510@...il.com>
> Acked-by: Chen-Yu Tsai <wens@...e.org>
> Acked-by: Rob Herring <robh@...nel.org>
> ---
>  Documentation/devicetree/bindings/clock/sunxi.txt |  1 +
>  drivers/clk/sunxi/clk-sunxi.c                     | 76 +++++++++++++++++++++++
>  2 files changed, 77 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/clock/sunxi.txt b/Documentation/devicetree/bindings/clock/sunxi.txt
> index 834436f..cba9fe55 100644
> --- a/Documentation/devicetree/bindings/clock/sunxi.txt
> +++ b/Documentation/devicetree/bindings/clock/sunxi.txt
> @@ -30,6 +30,7 @@ Required properties:
>  	"allwinner,sun6i-a31-ar100-clk" - for the AR100 on A31
>  	"allwinner,sun9i-a80-cpus-clk" - for the CPUS on A80
>  	"allwinner,sun6i-a31-ahb1-clk" - for the AHB1 clock on A31
> +	"allwinner,sun8i-a83t-ahb1-clk" - for the AHB1 clock on A83T
>  	"allwinner,sun8i-h3-ahb2-clk" - for the AHB2 clock on H3
>  	"allwinner,sun6i-a31-ahb1-gates-clk" - for the AHB1 gates on A31
>  	"allwinner,sun8i-a23-ahb1-gates-clk" - for the AHB1 gates on A23
> diff --git a/drivers/clk/sunxi/clk-sunxi.c b/drivers/clk/sunxi/clk-sunxi.c
> index 91de0a0..a7aab65 100644
> --- a/drivers/clk/sunxi/clk-sunxi.c
> +++ b/drivers/clk/sunxi/clk-sunxi.c
> @@ -344,6 +344,67 @@ static void sun6i_ahb1_recalc(struct factors_request *req)
>  	req->rate >>= req->p;
>  }
>  
> +#define SUN8I_A83T_AHB1_PARENT_PLL6	2
> +/**
> + * sun8i_a83t_get_ahb_factors() - calculates m, p factors for AHB
> + * AHB rate is calculated as follows
> + * rate = parent_rate >> p
> + *
> + * if parent is pll6, then
> + * parent_rate = pll6 rate / (m + 1)
> + */
> +
> +static void sun8i_a83t_get_ahb1_factors(struct factors_request *req)
> +{
> +	u8 div, calcp, calcm = 1;
> +
> +	/*
> +	 * clock can only divide, so we will never be able to achieve
> +	 * frequencies higher than the parent frequency
> +	 */
> +	if (req->parent_rate && req->rate > req->parent_rate)
> +		req->rate = req->parent_rate;
> +
> +	div = DIV_ROUND_UP(req->parent_rate, req->rate);
> +
> +	/* calculate pre-divider if parent is pll6 */
> +	if (req->parent_index >= SUN8I_A83T_AHB1_PARENT_PLL6) {
> +		if (div < 4)
> +			calcp = 0;
> +		else if (div / 2 < 4)
> +			calcp = 1;
> +		else if (div / 4 < 4)
> +			calcp = 2;
> +		else
> +			calcp = 3;
> +
> +		calcm = DIV_ROUND_UP(div, 1 << calcp);
> +	} else {
> +		calcp = __roundup_pow_of_two(div);
> +		calcp = calcp > 3 ? 3 : calcp;
> +	}
> +
> +	req->rate = (req->parent_rate / calcm) >> calcp;
> +	req->p = calcp;
> +	req->m = calcm - 1;
> +}
> +
> +/**
> +* sun8i_a83t_ahb1_recalc() - calculates AHB clock rate from m, p factors and
> +*			 parent index
> +*/
> +static void sun8i_a83t_ahb1_recalc(struct factors_request *req)
> +{
> +	req->rate = req->parent_rate;
> +
> +/* apply pre-divider first if parent is pll6 */

The comment indentation is wrong

> +	if (req->parent_index >= SUN6I_AHB1_PARENT_PLL6)

And this is not the right define you're using.

I still believe that duplicating the same logic just because of
different dividers is not the way to go.

You could solve that easily by adding a table for the muxes, and
associate it with parents and dividers, that you could store in
clk_factors.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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