linux-kernel - Re: [PATCH 4/4] cpufreq-dt: defer probing if OPP table is not ready

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Date:	Wed, 24 Dec 2014 10:58:21 -0600
From:	Nishanth Menon <nm@...com>
To:	Viresh Kumar <viresh.kumar@...aro.org>,
	Dmitry Torokhov <dtor@...omium.org>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Stefan Wahren <stefan.wahren@...e.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] cpufreq-dt: defer probing if OPP table is not ready

On 12/16/2014 10:37 PM, Viresh Kumar wrote:
> On 17 December 2014 at 04:39, Dmitry Torokhov <dtor@...omium.org> wrote:
>> cpufreq-dt driver supports mode when OPP table is provided by platform
>> code and not device tree. However on certain platforms code that fills
>> OPP table may run after cpufreq driver tries to initialize, so let's
>> report -EPROBE_DEFER if we do not find any entires in OPP table for the
>> CPU.
>>
>> Signed-off-by: Dmitry Torokhov <dtor@...omium.org>
>> ---
>>  drivers/cpufreq/cpufreq-dt.c | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c
>> index f56147a..fde97d6 100644
>> --- a/drivers/cpufreq/cpufreq-dt.c
>> +++ b/drivers/cpufreq/cpufreq-dt.c
>> @@ -211,6 +211,17 @@ static int cpufreq_init(struct cpufreq_policy *policy)
>>         /* OPPs might be populated at runtime, don't check for error here */
>>         of_init_opp_table(cpu_dev);
>>
>> +       /*
>> +        * But we need OPP table to function so if it is not there let's
>> +        * give platform code chance to provide it for us.
>> +        */
>> +       ret = dev_pm_opp_get_opp_count(cpu_dev);
>> +       if (ret <= 0) {
>> +               pr_debug("OPP table is not ready, deferring probe\n");
>> +               ret = -EPROBE_DEFER;
>> +               goto out_free_opp;
Umm.. why would I be here? because of_init_opp_table(cpu_dev) did not
find any OPPs at all. but that is OK, coz, we expect dynamic addition
of OPPs by someone else... now,

case 1:
if I did have few OPPs in DT (of_init_opp_table) and cpufreq_init gets
called *before* my dynamic OPPs are added(example based on efuse
entries) -> I'd already have built my dev_pm_opp_init_cpufreq_table
and that wont be accurate. but at that point dev_pm_opp_get_opp_count
cant fail either.. and if cpufreq_init was called *after* dynamic OPPs
are added - correct table, AND dev_pm_opp_get_opp_count wont fail either.

case 2:
If I had 0 OPPs in DT (of_init_opp_table fails) and cpufreq_init gets
called *before* my dynamic OPPs are added(example based on efuse
entries) -> doing a goto out_free_opp and of_free_opp_table is of no
use at all..

case 3:
If I had 0 OPPs in DT (of_init_opp_table fails) and cpufreq_init gets
called *after* my dynamic OPPs are added(example based on efuse
entries) -> I wont have error dev_pm_opp_get_opp_count.

So, you'd better want to introduce an intermediate goto for of_node_put

Also, please use dev_dbg instead of pr_*, since you already have
cpu_dev pointer.

>> +       }
>> +
>>         priv = kzalloc(sizeof(*priv), GFP_KERNEL);
>>         if (!priv) {
>>                 ret = -ENOMEM;
> 
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> 


-- 
Regards,
Nishanth Menon
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