linux-kernel - Re: [PATCH v4 3/8] clk: add support for clocks provided by SCP(System Control Processor)

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Message-ID: <5596A1B6.8020307@arm.com>
Date:	Fri, 03 Jul 2015 15:52:38 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	Stephen Boyd <sboyd@...eaurora.org>
CC:	Sudeep Holla <sudeep.holla@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	"Jon Medhurst (Tixy)" <tixy@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Kevin Hilman <khilman@...nel.org>,
	Olof Johansson <olof@...om.net>,
	Mike Turquette <mturquette@...aro.org>
Subject: Re: [PATCH v4 3/8] clk: add support for clocks provided by SCP(System
 Control Processor)

Hi Stephen,


Thanks for the review.

On 02/07/15 18:23, Stephen Boyd wrote:
> On 06/08, Sudeep Holla wrote:
>> diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
>> index 9897f353bf1a..0fe8daefc105 100644
>> --- a/drivers/clk/Kconfig
>> +++ b/drivers/clk/Kconfig
>> @@ -59,6 +59,16 @@ config COMMON_CLK_RK808
>>   	  clocked at 32KHz each. Clkout1 is always on, Clkout2 can off
>>   	  by control register.
>>
>> +config COMMON_CLK_SCPI
>> +        tristate "Clock driver controlled via SCPI interface"
>> +        depends on ARM_SCPI_PROTOCOL || COMPILE_TEST
>> +        ---help---
>> +          This driver provides support for clocks that are controlled
>> +          by firmware that implements the SCPI interface.
>> +
>> +	  This driver uses SCPI Message Protocol to interact with the
>> +	  firmware providing all the clock controls.
>
> The tabbing is weird here. Both paragraphs should have the same
> alignment.
>

Indeed, sorry for that, fixed now.

>> diff --git a/drivers/clk/clk-scpi.c b/drivers/clk/clk-scpi.c
>> new file mode 100644
>> index 000000000000..707b3430c55f
>> --- /dev/null
>> +++ b/drivers/clk/clk-scpi.c
>> +
>> +#include <linux/clk-provider.h>
>> +#include <linux/device.h>
>> +#include <linux/err.h>
>> +#include <linux/of.h>
>> +#include <linux/module.h>
>> +#include <linux/of_platform.h>
>> +#include <linux/scpi_protocol.h>
>
> Please include <linux/platform_device.h> as well.
>

Added now, didn't bother as of_platform.h includes it.

>> +
>> +struct scpi_clk {
>> +	u32 id;
>> +	const char *name;
>
> Do you need this? Or can you just use __clk_get_name() in places
> where the name is used?
>

Not used, so removed it.


[...]

>> +static long scpi_clk_round_rate(struct clk_hw *hw, unsigned long rate,
>> +				unsigned long *parent_rate)
>> +{
>
> Maybe a comment here like:
>
> /*
>   * We can't figure out what rate it will be, so just return the rate
>   * back to the caller. scpi_clk_recalc_rate() will be called
>   * after the rate is set and we'll know what rate the clock is
>   * running at then.
>   */
>

Done

>> +	return rate;
>> +}
>> +
>> +static int scpi_clk_set_rate(struct clk_hw *hw, unsigned long rate,
>> +			     unsigned long parent_rate)
>> +{
>> +	struct scpi_clk *clk = to_scpi_clk(hw);
>> +
>> +	return clk->scpi_ops->clk_set_val(clk->id, rate);
>> +}
>> +
>> +static void scpi_clk_disable(struct clk_hw *hw)
>> +{
>> +	scpi_clk_set_rate(hw, 0, 0);
>
> Does this mean you have to set a rate to enable the clock? Are
> you relying on drivers to call clk_set_rate() to implicitly
> enable the clock? If so, it would be better to cache the rate of
> the clock in set_rate if the clock isn't enabled in software and
> then send the cached rate during enable.
>

Agreed, I have asked the firmware/SCPI specification guys about
more details on what to expect from firmware. Once they get back,
will update the code considering your feedback.

[...]

>> +static int __scpi_find_dvfs_index(struct scpi_clk *clk, unsigned long rate)
>> +{
>> +	int idx, max_opp = clk->info->count;
>> +	struct scpi_opp *opp = clk->info->opps;
>
> const?
>

All the 3 above fixed now.

[...]

>> +
>> +	clk = devm_clk_register(dev, &sclk->hw);
>> +	if (!IS_ERR(clk) && max)
>> +		clk_set_rate_range(clk, min, max);
>
> Hm.. we're planning to make clk_register() return a struct
> clk_hw, so this will block that. We need some sort of clk_hw API
> that allows us to setup min/max limits on the clock from the
> provider side. Care to add that?
>

Can you provide pointer to the patches or the tree containing those
changes ? Are they targeted for v4.3 ?

Regards,
Sudeep
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