linux-kernel - Re: [PATCH 1/2] cpufreq: exynos4x12: Use the common clock framework to set APLL clock rate

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Date:	Thu, 26 Sep 2013 11:44:56 +0530
From:	Yadwinder Singh Brar <yadi.brar01@...il.com>
To:	Tomasz Figa <t.figa@...sung.com>
Cc:	Lukasz Majewski <l.majewski@...sung.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Lukasz Majewski <l.majewski@...ess.pl>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Myungjoo Ham <myungjoo.ham@...sung.com>,
	Kukjin Kim <kgene@...nel.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH 1/2] cpufreq: exynos4x12: Use the common clock framework
 to set APLL clock rate

Hi Tomasz,

>> On Wed, Sep 25, 2013 at 4:52 PM, Lukasz Majewski <l.majewski@...sung.com> wrote:
>> > In the exynos4x12_set_apll() function, the APLL frequency is set with
>> > direct register manipulation.
>> >
>> > Such approach is not allowed in the common clock framework. The frequency
>> > is changed, but the corresponding clock value is not updated. This causes
>> > wrong frequency read from cpufreq's cpuinfo_cur_freq sysfs attribute.
>> >
>>
>> This patch looks incomplete, leaving the driver in untidy state, perhaps its
>> doesn't fix the above stated problem completely. what about
>> if (!exynos4x12_pms_change(old_index, new_index)) becomes true?
>>
>> IMHO, this driver needs lot more work in addition to this patch to cleanly and
>> completely move the cpufreq driver to common clock framework.
>
> I agree that the other case needs to be handled as well. Basically the
> whole conditional block dependent on exynos4x12_pms_change() can be safely
> dropped, because this condition is already handled in PLL driver.
>

Exactly!

> Lukasz is already working on further rework of this driver to clean it up
> from legacy code, but this will have to wait for 3.13, as 3.12 is already
> in rc stage and only fixes can be accepted for it.
>
>> For fixing this issue urgently, setting CLK_GET_RATE_NOCACHE for apll
>> in clk driver can also be quicker fix.
>
> Unfortunately this is not how this flag works. It only makes
> clk_get_rate() call ->recalc_rate() operation of the clock instead of
> instantly returning cached rate - it doesn't seem to work recursively.
>

hmm.. yes it can't help in our case as it recursively walks only the subtree
of clk but in our case we are changing rate of parent.

Regards,
Yadwinder
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