linux-kernel - Re: [PATCH 2/2] fsi/sbefifo: Fix reset timeout

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Message-ID: <CACPK8XcnyO+T18W0pk6dRahg1aanaJYsVfxtXtZN31phub+=TQ@mail.gmail.com>
Date:   Thu, 10 Sep 2020 03:08:04 +0000
From:   Joel Stanley <joel@....id.au>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     linux-fsi@...ts.ozlabs.org, Joachim Fenkes <fenkes@...ibm.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alistar Popple <alistair@...ple.id.au>
Subject: Re: [PATCH 2/2] fsi/sbefifo: Fix reset timeout

On Fri, 24 Jul 2020 at 14:34, Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 7/24/20 12:15 AM, Joel Stanley wrote:
> > From: Joachim Fenkes <FENKES@...ibm.com>
> >
> > On BMCs with lower timer resolution than 1ms, msleep(1) will take
> > way longer than 1ms, so looping 10k times won't wait for 10s but
> > significantly longer.
> >
> > Fix this by using jiffies like the rest of the code.
> >
> > Fixes: 9f4a8a2d7f9d ("fsi/sbefifo: Add driver for the SBE FIFO")
> > Signed-off-by: Joachim Fenkes <fenkes@...ibm.com>
> > Signed-off-by: Joel Stanley <joel@....id.au>
> > ---
> >  drivers/fsi/fsi-sbefifo.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/fsi/fsi-sbefifo.c b/drivers/fsi/fsi-sbefifo.c
> > index 655b45c1f6ba..3ad9510ad4a4 100644
> > --- a/drivers/fsi/fsi-sbefifo.c
> > +++ b/drivers/fsi/fsi-sbefifo.c
> > @@ -325,6 +325,7 @@ static int sbefifo_up_write(struct sbefifo *sbefifo, __be32 word)
> >  static int sbefifo_request_reset(struct sbefifo *sbefifo)
> >  {
> >       struct device *dev = &sbefifo->fsi_dev->dev;
> > +     unsigned long end_time;
> >       u32 status, timeout;
> >       int rc;
> >
> > @@ -341,7 +342,8 @@ static int sbefifo_request_reset(struct sbefifo *sbefifo)
> >       }
> >
> >       /* Wait for it to complete */
> > -     for (timeout = 0; timeout < SBEFIFO_RESET_TIMEOUT; timeout++) {
> > +     end_time = jiffies + msecs_to_jiffies(SBEFIFO_RESET_TIMEOUT);
> > +     while (!time_after(jiffies, end_time)) {
> >               rc = sbefifo_regr(sbefifo, SBEFIFO_UP | SBEFIFO_STS, &status);
> >               if (rc) {
> >                       dev_err(dev, "Failed to read UP fifo status during reset"
> > @@ -355,7 +357,7 @@ static int sbefifo_request_reset(struct sbefifo *sbefifo)
> >                       return 0;
> >               }
> >
> > -             msleep(1);
> > +             cond_resched();
>
> A hot loop ? Are you sure ? usleep_range() might make more sense here.

Thanks for the review.

Joachim, I can fix this up for you.

Do you have a suggestion for how long to wait? What's the best case
completion time for a sbe reset?

We also have a hot loop in sbefifo_wait. I'm open to suggestions for
how long that should delay for.

Cheers,

Joel