linux-kernel - Re: [PATCH AUTOSEL 4.19 080/106] mips: Add udelay lpj numbers adjustment

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Message-ID: <20200711100149.GA2397222@aurel32.net>
Date:   Sat, 11 Jul 2020 12:01:49 +0200
From:   Aurelien Jarno <aurelien@...el32.net>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-mips@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 4.19 080/106] mips: Add udelay lpj numbers
 adjustment

On 2020-06-08 19:22, Sasha Levin wrote:
> From: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> 
> [ Upstream commit ed26aacfb5f71eecb20a51c4467da440cb719d66 ]
> 
> Loops-per-jiffies is a special number which represents a number of
> noop-loop cycles per CPU-scheduler quantum - jiffies. As you
> understand aside from CPU-specific implementation it depends on
> the CPU frequency. So when a platform has the CPU frequency fixed,
> we have no problem and the current udelay interface will work
> just fine. But as soon as CPU-freq driver is enabled and the cores
> frequency changes, we'll end up with distorted udelay's. In order
> to fix this we have to accordinly adjust the per-CPU udelay_val
> (the same as the global loops_per_jiffy) number. This can be done
> in the CPU-freq transition event handler. We subscribe to that event
> in the MIPS arch time-inititalization method.
> 
> Co-developed-by: Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>
> Signed-off-by: Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> Reviewed-by: Jiaxun Yang <jiaxun.yang@...goat.com>
> 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: devicetree@...r.kernel.org
> Signed-off-by: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  arch/mips/kernel/time.c | 70 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 70 insertions(+)
> 
> diff --git a/arch/mips/kernel/time.c b/arch/mips/kernel/time.c
> index bfe02ded25d1..1e631a484ddf 100644
> --- a/arch/mips/kernel/time.c
> +++ b/arch/mips/kernel/time.c
> @@ -22,12 +22,82 @@
>  #include <linux/smp.h>
>  #include <linux/spinlock.h>
>  #include <linux/export.h>
> +#include <linux/cpufreq.h>
> +#include <linux/delay.h>
>  
>  #include <asm/cpu-features.h>
>  #include <asm/cpu-type.h>
>  #include <asm/div64.h>
>  #include <asm/time.h>
>  
> +#ifdef CONFIG_CPU_FREQ
> +
> +static DEFINE_PER_CPU(unsigned long, pcp_lpj_ref);
> +static DEFINE_PER_CPU(unsigned long, pcp_lpj_ref_freq);
> +static unsigned long glb_lpj_ref;
> +static unsigned long glb_lpj_ref_freq;
> +
> +static int cpufreq_callback(struct notifier_block *nb,
> +			    unsigned long val, void *data)
> +{
> +	struct cpufreq_freqs *freq = data;
> +	struct cpumask *cpus = freq->policy->cpus;
                                     ^^^^^^

The policy member has been added in kernel 5.2, so kernel 4.19.129 and
later do not build anymore when CONFIG_CPU_FREQ=y.

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@...el32.net                 http://www.aurel32.net