linux-kernel - Re: [PATCH 2/2] cpufreq: brcmstb-avs-cpufreq: prefer SCMI cpufreq if supported

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Date:   Thu, 19 Apr 2018 15:10:45 -0700
From:   Markus Mayer <mmayer@...adcom.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Brian Norris <computersforpeace@...il.com>,
        Gregory Fong <gregory.0xf0@...il.com>,
        Jim Quinlan <jim2101024@...il.com>,
        Broadcom Kernel List <bcm-kernel-feedback-list@...adcom.com>,
        Power Management List <linux-pm@...r.kernel.org>,
        ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] cpufreq: brcmstb-avs-cpufreq: prefer SCMI cpufreq if supported

On 18 April 2018 at 09:37, Florian Fainelli <f.fainelli@...il.com> wrote:
> On 04/18/2018 08:56 AM, Markus Mayer wrote:
>> From: Jim Quinlan <jim2101024@...il.com>
>>
>> If the SCMI cpufreq driver is supported, we bail, so that the new
>> approach can be used.
>>
>> Signed-off-by: Jim Quinlan <jim2101024@...il.com>
>> Signed-off-by: Markus Mayer <mmayer@...adcom.com>
>> ---
>>  drivers/cpufreq/brcmstb-avs-cpufreq.c | 16 ++++++++++++++++
>>  1 file changed, 16 insertions(+)
>>
>> diff --git a/drivers/cpufreq/brcmstb-avs-cpufreq.c b/drivers/cpufreq/brcmstb-avs-cpufreq.c
>> index b07559b9ed99..b4861a730162 100644
>> --- a/drivers/cpufreq/brcmstb-avs-cpufreq.c
>> +++ b/drivers/cpufreq/brcmstb-avs-cpufreq.c
>> @@ -164,6 +164,8 @@
>>  #define BRCM_AVS_CPU_INTR    "brcm,avs-cpu-l2-intr"
>>  #define BRCM_AVS_HOST_INTR   "sw_intr"
>>
>> +#define ARM_SCMI_COMPAT              "arm,scmi"
>> +
>>  struct pmap {
>>       unsigned int mode;
>>       unsigned int p1;
>> @@ -511,6 +513,20 @@ static int brcm_avs_prepare_init(struct platform_device *pdev)
>>       struct device *dev;
>>       int host_irq, ret;
>>
>> +     /*
>> +      * If the SCMI cpufreq driver is supported, we bail, so that the more
>> +      * modern approach can be used.
>> +      */
>> +     if (IS_ENABLED(CONFIG_ARM_SCMI_PROTOCOL)) {
>> +             struct device_node *np;
>> +
>> +             np = of_find_compatible_node(NULL, NULL, ARM_SCMI_COMPAT);
>> +             if (np) {
>> +                     of_node_put(np);
>> +                     return -ENXIO;
>> +             }
>
> We would probably want to make sure that the node is also enabled (that
> is, does not have a status = "disabled" property) otherwise the check
> can be defeated. Something like:
>
>                 if (np && of_device_is_available(np))

Would we want something like this instead?

                 if (np) {
                                  bool bail_early =
(of_device_is_available(np) > 0);

                                  of_node_put(np);
                                  if (bail_early)
                                          return -ENXIO;
                 }

To ensure of_node_put() is called?

> should be good for that.
>
> Thanks!
> --
> Florian