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

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Date:   Tue, 8 Nov 2016 09:52:25 +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

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.