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

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Date:	Mon, 4 Apr 2016 11:07:29 +0800
From:	Vishnu Patekar <vishnupatekar0510@...il.com>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	Emilio Lopez <emilio@...pez.com.ar>,
	Jens Kuske <jenskuske@...il.com>,
	Hans de Goede <hdegoede@...hat.com>,
	Chen-Yu Tsai <wens@...e.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-sunxi@...glegroups.com" <linux-sunxi@...glegroups.com>,
	linux-gpio@...r.kernel.org,
	Linus Walleij <linus.walleij@...aro.org>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Reinder de Haan <patchesrdh@...as.com>,
	linux-clk <linux-clk@...r.kernel.org>
Subject: Re: [PATCH v4 02/13] clk: sunxi: add ahb1 clock for A83T

Hello Maxime,

On Thu, Mar 17, 2016 at 6:40 PM, Maxime Ripard
<maxime.ripard@...e-electrons.com> wrote:
> 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.

I've similar solution (please ignore a83 specific functions those will
be common for a31 and a83t).
https://github.com/vishnupatekar/linux/commit/f7de5b48d886a672b1f6db112fbfd5d2c9849afa

is it aligned to what you're saying?

Or do you mean we can use mux clock with div clock as composite clock?
>
> Maxime
>
> --
> Maxime Ripard, Free Electrons
> Embedded Linux, Kernel and Android engineering
> http://free-electrons.com