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

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Message-ID: <6741c61b-e557-5063-2bad-2464eccfc639@i2se.com>
Date:   Wed, 31 May 2017 10:59:46 +0200
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

Am 31.05.2017 um 10:28 schrieb Phil Elwell:
> Hi Stefan,
>
> On 30/05/2017 19:41, Stefan Wahren wrote:
>> 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.
> Sure - good idea.
>
>>> 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.
> Yes, will do.
>
>>> +	"-",
>>> +	"xosc",
>>> +	"-",
>>> +	"-",
>>> +	"-",
>>> +	"-",
>>> +	"plld_per",
>>> +};
>> Is there a dummy entry for "pllh_aux" missing?
> Yes and no - adding it will cause an extra iteration around the loop, but 
> perhaps it's less confusing. I'll add one.

In case you want to save an iteration, you could add short comment
instead of a dummy entry.

>
>>> +
>>>  #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__)
> Of course - no problem.
>
> Thanks for the feedback - it will be incorporated into V2.
>
> Phil