linux-kernel - Re: [PATCH v1 1/1] mmc: mmc_spi: Simplify busy loop in mmc_spi

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Message-ID: <CAPDyKFoM-gkFPoFePbHS62r-HUpk6ipA5J-qPbQ8NWL9Mm_N2Q@mail.gmail.com>
Date:   Thu, 8 Jul 2021 14:31:37 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-mmc <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/1] mmc: mmc_spi: Simplify busy loop in mmc_spi_skip()

On Wed, 23 Jun 2021 at 12:17, Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> Infinite loops are hard to read and understand because of
> hidden main loop condition. Simplify such one in mmc_spi_skip().
>
> Using schedule() to schedule (and be friendly to others)
> is discouraged and cond_resched() should be used instead.
> Hence, replace schedule() with cond_resched() at the same
> time.
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  drivers/mmc/host/mmc_spi.c | 15 ++++-----------
>  1 file changed, 4 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
> index 65c65bb5737f..a1bcde3395a6 100644
> --- a/drivers/mmc/host/mmc_spi.c
> +++ b/drivers/mmc/host/mmc_spi.c
> @@ -180,7 +180,7 @@ static int mmc_spi_skip(struct mmc_spi_host *host, unsigned long timeout,
>         u8 *cp = host->data->status;
>         unsigned long start = jiffies;
>
> -       while (1) {
> +       do {
>                 int             status;
>                 unsigned        i;
>
> @@ -193,16 +193,9 @@ static int mmc_spi_skip(struct mmc_spi_host *host, unsigned long timeout,
>                                 return cp[i];
>                 }
>
> -               if (time_is_before_jiffies(start + timeout))
> -                       break;
> -
> -               /* If we need long timeouts, we may release the CPU.
> -                * We use jiffies here because we want to have a relation
> -                * between elapsed time and the blocking of the scheduler.
> -                */
> -               if (time_is_before_jiffies(start + 1))
> -                       schedule();
> -       }
> +               /* If we need long timeouts, we may release the CPU */
> +               cond_resched();
> +       } while (time_is_after_jiffies(start + timeout));

This certainly is an improvement.

Although, what do you think of moving to readx_poll_timeout(), that
should allow even a better cleanup, don't you think?

>         return -ETIMEDOUT;
>  }
>

Kind regards
Uffe