linux-kernel - Re: [PATCH 1/6] clk: stm32f4: Add PLL_I2S & PLL

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Message-ID: <CAFvLkMSUg8=nYY9Zm2Q4ZW=GqUaczK_TA5b5jjb45vYyhoVLZA@mail.gmail.com>
Date:   Wed, 9 Nov 2016 09:10:25 +0100
From:   Radosław Pietrzyk <radoslaw.pietrzyk@...il.com>
To:     Gabriel Fernandez <gabriel.fernandez@...com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Nicolas Pitre <nico@...aro.org>, Arnd Bergmann <arnd@...db.de>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Andrea Merello <andrea.merello@...il.com>,
        devicetree@...r.kernel.org, amelie.delaunay@...com,
        kernel@...inux.com, olivier.bideau@...com,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
        ludovic.barre@...com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/6] clk: stm32f4: Add PLL_I2S & PLL_SAI for STM32F429/469 boards

I would expect that VCO clock will force recalculation for all its
children if I am not mistaken.

2016-11-08 17:19 GMT+01:00 Gabriel Fernandez <gabriel.fernandez@...com>:
> On 11/08/2016 09:52 AM, Radosław Pietrzyk wrote:
>>
>> 2016-11-08 9:35 GMT+01:00 Gabriel Fernandez <gabriel.fernandez@...com>:
>>>
>>> Hi Radosław
>>>
>>> Many thanks for reviewing.
>>>
>>> On 11/07/2016 03:57 PM, Radosław Pietrzyk wrote:
>>>>>
>>>>> +static struct clk_hw *clk_register_pll_div(const char *name,
>>>>> +               const char *parent_name, unsigned long flags,
>>>>> +               void __iomem *reg, u8 shift, u8 width,
>>>>> +               u8 clk_divider_flags, const struct clk_div_table
>>>>> *table,
>>>>> +               struct clk_hw *pll_hw, spinlock_t *lock)
>>>>> +{
>>>>> +       struct stm32f4_pll_div *pll_div;
>>>>> +       struct clk_hw *hw;
>>>>> +       struct clk_init_data init;
>>>>> +       int ret;
>>>>> +
>>>>> +       /* allocate the divider */
>>>>> +       pll_div = kzalloc(sizeof(*pll_div), GFP_KERNEL);
>>>>> +       if (!pll_div)
>>>>> +               return ERR_PTR(-ENOMEM);
>>>>> +
>>>>> +       init.name = name;
>>>>> +       init.ops = &stm32f4_pll_div_ops;
>>>>> +       init.flags = flags;
>>>>
>>>> Maybe it's worth to have CLK_SET_RATE_PARENT here and the VCO clock
>>>> should have CLK_SET_RATE_GATE flag and we can get rid of custom
>>>> divider ops.
>>>
>>> I don't want to offer the possibility to change the vco clock through the
>>> divisor of the pll (only by a boot-loader or by DT).
>>>
>>> e.g. if i make a set rate on lcd-tft clock, i don't want to change the
>>> SAI
>>> frequencies.
>>>
>>> I used same structure for internal divisors of the pll (p, q, r) and for
>>> post divisors (plli2s-q-div, pllsai-q-div & pllsai-r-div).
>>> That why the CLK_SET_RATE_PARENT flag is transmit by parameter.
>>>
>>> These divisors are similar because we have to switch off the pll before
>>> changing the rate.
>>>
>> But changing pll and lcd dividers only may not be enough for getting
>> very specific pixelclocks and that might require changing the VCO
>> frequency itself. The rest of the SAI tree should be recalculated
>> then.
>
> I agree but it seems to be too much complicated to recalculate all PLL
> divisors if we change the vco clock.
> You mean to use Clock notifier callback ?