linux-kernel - Re: [PATCH 2/3] watchdog: sprd: change timeout value from 1000 to 2000

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Message-ID: <CAAfSe-v1Qt1KG0DowigYWG=pK2abQ5UzQv4FqWRq8_YzYqKz7Q@mail.gmail.com>
Date:   Tue, 27 Oct 2020 17:21:06 +0800
From:   Chunyan Zhang <zhang.lyra@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        linux-watchdog@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Orson Zhai <orsonzhai@...il.com>,
        Baolin Wang <baolin.wang7@...il.com>,
        Chunyan Zhang <chunyan.zhang@...soc.com>,
        jingchao.ye@...soc.com, ling_ling.xu@...soc.com,
        xiaoqing.wu@...soc.com
Subject: Re: [PATCH 2/3] watchdog: sprd: change timeout value from 1000 to 2000

On Mon, 26 Oct 2020 at 22:36, Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 10/26/20 1:09 AM, Chunyan Zhang wrote:
> > From: Lingling Xu <ling_ling.xu@...soc.com>
> >
> > Because cpu_relax() takes different time on different SoCs, for some rare
> > cases, it would take more than 1000 cycles for waitting load operation
>
> waiting

Ok.

>
> > finished. The result of many times testing verified that changing the
> > timeout value to 2000 can solve the issue.
> >
>
> This is just a kludge that doesn't address the underlying problem.
> As the wait loop states, "Waiting the load value operation done,
> it needs two or three RTC clock cycles". This means the loop
> should wait for a maximum number of clock cycles, and not run
> as hot loop. If we assume that clk_get_rate() returns the clock
> frequency, that frequency can be used to determine how long this
> needs to be retried. It might also make sense - depending on how
> long this actually takes - to use usleep_range() instead of
> cpu_relax() to avoid the hot loop.

Agree, using usleep_range() instead makes more sense, I will look into that.

Thanks for your review.

Chunyan

>
> Guenter
>
> > Fixes: 477603467009 ("watchdog: Add Spreadtrum watchdog driver")
> > Signed-off-by: Lingling Xu <ling_ling.xu@...soc.com>
> > Signed-off-by: Chunyan Zhang <chunyan.zhang@...soc.com>
> > ---
> >  drivers/watchdog/sprd_wdt.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/watchdog/sprd_wdt.c b/drivers/watchdog/sprd_wdt.c
> > index f3c90b4afead..4f2a8c6d6485 100644
> > --- a/drivers/watchdog/sprd_wdt.c
> > +++ b/drivers/watchdog/sprd_wdt.c
> > @@ -53,7 +53,7 @@
> >
> >  #define SPRD_WDT_CNT_HIGH_SHIFT              16
> >  #define SPRD_WDT_LOW_VALUE_MASK              GENMASK(15, 0)
> > -#define SPRD_WDT_LOAD_TIMEOUT                1000
> > +#define SPRD_WDT_LOAD_TIMEOUT                2000
> >
> >  struct sprd_wdt {
> >       void __iomem *base;
> >
>