linux-kernel - Re: [PATCH 1/2] clk: bcm2835: Limit PCM clock to OSC and PLLD

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Date:   Tue, 30 May 2017 20:41:05 +0200 (CEST)
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Phil Elwell <phil@...pberrypi.org>, linux-clk@...r.kernel.org,
        Eric Anholt <eric@...olt.net>, linux-kernel@...r.kernel.org,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        linux-rpi-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] clk: bcm2835: Limit PCM clock to OSC and PLLD_PER

Hi Phil,

> Phil Elwell <phil@...pberrypi.org> hat am 30. Mai 2017 um 18:28 geschrieben:
> 
> 
> Restrict clock sources for the PCM peripheral to the oscillator and
> PLLD_PER because other source may have varying rates or be switched off.

> Prevent other sources from being selected by replacing their names in
> the list of potential parents with dummy entries (entry index is
> significant).

i like to have this as a comment above the definition of bcm2835_pcm_per_parents.

> 
> Signed-off-by: Phil Elwell <phil@...pberrypi.org>
> ---
>  drivers/clk/bcm/clk-bcm2835.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
> index 0258538..facc346 100644
> --- a/drivers/clk/bcm/clk-bcm2835.c
> +++ b/drivers/clk/bcm/clk-bcm2835.c
> @@ -1511,6 +1511,16 @@ struct bcm2835_clk_desc {
>  	"pllh_aux",
>  };
>
> +static const char *const bcm2835_pcm_per_parents[] = {

As mentioned above, there should be a comment like all the others. 

> +	"-",
> +	"xosc",
> +	"-",
> +	"-",
> +	"-",
> +	"-",
> +	"plld_per",
> +};

Is there a dummy entry for "pllh_aux" missing?

> +
>  #define REGISTER_PER_CLK(...)	REGISTER_CLK(				\
>  	.num_mux_parents = ARRAY_SIZE(bcm2835_clock_per_parents),	\
>  	.parents = bcm2835_clock_per_parents,				\
> @@ -2000,6 +2010,7 @@ struct bcm2835_clk_desc {
>  		.int_bits = 12,
>  		.frac_bits = 12,
>  		.is_mash_clock = true,
> +		.parents = bcm2835_pcm_per_parents,

This looks a little bit hacky to me. Not sure, but can we do something like this?

#define REGISTER_PCM_CLK(...)	REGISTER_CLK(				\
	.num_mux_parents = ARRAY_SIZE(bcm2835_pcm_per_parents),	\
	.parents = bcm2835_pcm_per_parents,				\
	__VA_ARGS__)

Regards
Stefan

>  		.tcnt_mux = 23),
>  	[BCM2835_CLOCK_PWM]	= REGISTER_PER_CLK(
>  		.name = "pwm",
> -- 
> 1.9.1
>