linux-kernel - Re: [PATCH v2 20/20] cpufreq: Return zero on success in boost sw setting

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Date:   Fri, 15 May 2020 17:58:47 +0200
From:   "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
To:     Sergey.Semin@...kalelectronics.ru,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Matthias Kaehlcke <mka@...omium.org>
Cc:     Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Paul Burton <paulburton@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>, linux-mips@...r.kernel.org,
        devicetree@...r.kernel.org, stable@...r.kernel.org,
        Frederic Weisbecker <frederic@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, Yue Hu <huyue2@...ong.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 20/20] cpufreq: Return zero on success in boost sw
 setting

On 5/6/2020 7:42 PM, Sergey.Semin@...kalelectronics.ru wrote:
> From: Serge Semin <Sergey.Semin@...kalelectronics.ru>
>
> Recent commit e61a41256edf ("cpufreq: dev_pm_qos_update_request() can
> return 1 on success") fixed a problem when active policies traverse
> was falsely stopped due to invalidly treating the non-zero return value
> from freq_qos_update_request() method as an error. Yes, that function
> can return positive values if the requested update actually took place.
> The current problem is that the returned value is then passed to the
> return cell of the cpufreq_boost_set_sw() (set_boost callback) method.
> This value is then also analyzed for being non-zero, which is also
> treated as having an error. As a result during the boost activation
> we'll get an error returned while having the QOS frequency update
> successfully performed. Fix this by returning a negative value from the
> cpufreq_boost_set_sw() if actual error was encountered and zero
> otherwise treating any positive values as the successful operations
> completion.
>
> Fixes: 18c49926c4bf ("cpufreq: Add QoS requests for userspace constraints")
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>
> Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Cc: Paul Burton <paulburton@...nel.org>
> Cc: Ralf Baechle <ralf@...ux-mips.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: linux-mips@...r.kernel.org
> Cc: devicetree@...r.kernel.org
> Cc: stable@...r.kernel.org
> ---
>   drivers/cpufreq/cpufreq.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 045f9fe157ce..5870cdca88cf 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2554,7 +2554,7 @@ static int cpufreq_boost_set_sw(int state)
>   			break;
>   	}
>   
> -	return ret;
> +	return ret < 0 ? ret : 0;
>   }
>   
>   int cpufreq_boost_trigger_state(int state)

IMO it is better to update the caller of this function to handle the 
positive value possibly returned by it correctly.

Thanks!