linux-kernel - Re: [PATCH v4 12/19] cpufreq: cpufreq-cpu0: remove device tree parsing for cpu nodes

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Date:	Mon, 09 Sep 2013 10:24:39 +0100
From:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Shawn Guo <shawn.guo@...aro.org>
CC:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jonas Bonn <jonas@...thpole.se>,
	Michal Simek <monstr@...str.eu>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>
Subject: Re: [PATCH v4 12/19] cpufreq: cpufreq-cpu0: remove device tree parsing
 for cpu nodes

On 06/09/13 14:44, Guennadi Liakhovetski wrote:
> Hi
> 
> On Tue, 20 Aug 2013, Sudeep KarkadaNagesha wrote:
> 
>> From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>
>>
>> Now that the cpu device registration initialises the of_node(if available)
>> appropriately for all the cpus, parsing here is redundant.
>>
>> This patch removes all DT parsing and uses cpu->of_node instead.
>>
>> Acked-by: Shawn Guo <shawn.guo@...aro.org>
>> Acked-by: Rob Herring <rob.herring@...xeda.com>
>> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
>> Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>
>> ---
>>  drivers/cpufreq/cpufreq-cpu0.c | 23 ++++-------------------
>>  1 file changed, 4 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/cpufreq/cpufreq-cpu0.c b/drivers/cpufreq/cpufreq-cpu0.=
>> c
>> index ad1fde2..5b05c26 100644
>> --- a/drivers/cpufreq/cpufreq-cpu0.c
>> +++ b/drivers/cpufreq/cpufreq-cpu0.c
>> @@ -174,29 +174,17 @@ static struct cpufreq_driver cpu0_cpufreq_driver =3D =
>> {
>> =20
>>  static int cpu0_cpufreq_probe(struct platform_device *pdev)
>>  {
>> -=09struct device_node *np, *parent;
>> +=09struct device_node *np;
>>  =09int ret;
>> =20
>> -=09parent =3D of_find_node_by_path("/cpus");
>> -=09if (!parent) {
>> -=09=09pr_err("failed to find OF /cpus\n");
>> -=09=09return -ENOENT;
>> -=09}
>> -
>> -=09for_each_child_of_node(parent, np) {
>> -=09=09if (of_get_property(np, "operating-points", NULL))
>> -=09=09=09break;
>> -=09}
>> +=09cpu_dev =3D &pdev->dev;
>> =20
>> +=09np =3D of_node_get(cpu_dev->of_node);
> 
> Has this actually been tested? This seems to break cpufreq-cpu0. The 
> reason is, that this probe function is called not for the DT CPU node, but 
> for a special virtual cpufreq-cpu0 platform device, typically created by 
> platforms, using
> 
> 	platform_device_register_simple("cpufreq-cpu0", -1, NULL, 0);
> 
> which then of course doesn't have on .of_node associated with it.
> 

Hi Guennadi,

Based on my understanding of the original code:
        cpu_dev = &pdev->dev;
	...
	ret = of_init_opp_table(cpu_dev);

of_init_opp_table needs cpu_dev to be get_cpu_device(0). My
understanding was that platform using cpufreq-cpu0 sets &pdev->dev to
get_cpu_device(0). But looks like that's not the case.

Hi Shawn,

Can you please clarify ? The fix would be as below but I would like to
know if setting cpu_dev to get_cpu_device(0) instead of &pdev->dev has
any impact on other parts of code using cpu_dev ?

diff --git a/drivers/cpufreq/cpufreq-cpu0.c b/drivers/cpufreq/cpufreq-cpu0.c
index cbfffa9..871c336 100644
--- a/drivers/cpufreq/cpufreq-cpu0.c
+++ b/drivers/cpufreq/cpufreq-cpu0.c
@@ -177,7 +177,7 @@ static int cpu0_cpufreq_probe(struct platform_device
*pdev)
        struct device_node *np;
        int ret;

-       cpu_dev = &pdev->dev;
+       cpu_dev = get_cpu_device(0);

        np = of_node_get(cpu_dev->of_node);
        if (!np) {


Regards,
Sudeep



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