linux-kernel - Re: [PATCH v2 17/20] mips: Add udelay lpj numbers adjustment

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Date:   Fri, 8 May 2020 20:15:34 +0800
From:   Jiaxun Yang <jiaxun.yang@...goat.com>
To:     <Sergey.Semin@...kalelectronics.ru>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        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-pm@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Allison Randal <allison@...utok.net>,
        <linux-mips@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 17/20] mips: Add udelay lpj numbers adjustment

On Wed, 6 May 2020 20:42:35 +0300
<Sergey.Semin@...kalelectronics.ru> wrote:

> From: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> 
> 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>
> 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-pm@...r.kernel.org
> Cc: devicetree@...r.kernel.org

Reviewed-by: Jiaxun Yang <jiaxun.yang@...goat.com>

That have been absent in MIPS kernel so long!

Thanks.
> ---
[...]
---
Jiaxun Yang