linux-kernel - Re: [PATCH] Reorganize STM32 clocks in order to prepare them for PLLI2S and PLLSAI

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Date:   Mon, 10 Oct 2016 10:37:45 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     radek <radoslaw.pietrzyk@...il.com>, mturquette@...libre.com,
        sboyd@...eaurora.org, mcoquelin.stm32@...il.com,
        alexandre.torgue@...com
Cc:     linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Reorganize STM32 clocks in order to prepare them for
 PLLI2S and PLLSAI

On 06/10/16 23:01, radek wrote:
> From: Radoslaw Pietrzyk <radoslaw.pietrzyk@...il.com>
>
> Signed-off-by: Radoslaw Pietrzyk <radoslaw.pietrzyk@...il.com>
> ---
>  drivers/clk/clk-stm32f4.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/clk/clk-stm32f4.c b/drivers/clk/clk-stm32f4.c
> index 02d6810..1fd3eac 100644
> --- a/drivers/clk/clk-stm32f4.c
> +++ b/drivers/clk/clk-stm32f4.c
> @@ -245,9 +245,10 @@ static void stm32f4_rcc_register_pll(const char *hse_clk, const char *hsi_clk)
>  	const char   *pllsrc = pllcfgr & BIT(22) ? hse_clk : hsi_clk;
>  	unsigned long pllq   = (pllcfgr >> 24) & 0xf;
>
> -	clk_register_fixed_factor(NULL, "vco", pllsrc, 0, plln, pllm);
> -	clk_register_fixed_factor(NULL, "pll", "vco", 0, 1, pllp);
> -	clk_register_fixed_factor(NULL, "pll48", "vco", 0, 1, pllq);
> +	clk_register_fixed_factor(NULL, "vco-div", pllsrc, 0, 1, pllm);
> +	clk_register_fixed_factor(NULL, "vco-mul", "vco-div", 0, plln, 1);
> +	clk_register_fixed_factor(NULL, "pll", "vco-mul", 0, 1, pllp);
> +	clk_register_fixed_factor(NULL, "pll48", "vco-mul", 0, 1, pllq);

I'm struggling to marry this up to the clock tree diagram for the 
F4-series (and there's no patch description to help me).

I can see the value of naming the "/M" pre-division separately (and 
agree that its hard to find it a good name for this clock in the 
datasheet). However I am struggling to work out why we'd want to rename 
the vco output.

For me the names for the multiplies clock within each pll emerges fairly 
cleanly from the datasheet (PLL -> vco, PLLI2S -> vcoi2s, PLLSAI -> 
vcosai). What does the '-mul' add?


Daniel.