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

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Date:   Tue, 8 Nov 2016 17:19:13 +0100
From:   Gabriel Fernandez <gabriel.fernandez@...com>
To:     Radosław Pietrzyk <radoslaw.pietrzyk@...il.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

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 ?