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    SubjectRe: [PATCH] mmc: sdhci: use udelay instead of mdelay
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    On Monday, May 30, 2016 7:55:55 AM CEST Baranowska, BeataX wrote:
    > From: Chuanxiao Dong <chuanxiao.dong@intel.com>
    >
    > This patch will use udelay instead of mdelay when waiting for
    > SDHCI hardware to be stable. udelay can help to reduce the waiting
    > time when is in critical region which is protected by spinlock.
    >
    > With this patch, __sdhci_set_ios only take a few microseconds to be
    > done.
    >
    > Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
    > ---
    > drivers/mmc/host/sdhci.c | 18 +++++++++---------
    > 1 file changed, 9 insertions(+), 9 deletions(-)
    >
    > diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
    > index e010ea4eb6f5..56d2c7567d97 100644
    > --- a/drivers/mmc/host/sdhci.c
    > +++ b/drivers/mmc/host/sdhci.c
    > @@ -173,8 +173,8 @@ void sdhci_reset(struct sdhci_host *host, u8 mask)
    > sdhci_runtime_pm_bus_off(host);
    > }
    >
    > - /* Wait max 100 ms */
    > - timeout = 100;
    > + /* Wait max 10000 ms */
    > + timeout = 10000;
    >
    > /* hw clears the bit when it's done */
    > while (sdhci_readb(host, SDHCI_SOFTWARE_RESET) & mask) {
    > @@ -185,7 +185,7 @@ void sdhci_reset(struct sdhci_host *host, u8 mask)
    > return;
    > }
    > timeout--;
    > - mdelay(1);
    > + udelay(10);
    > }
    > }
    > EXPORT_SYMBOL_GPL(sdhci_reset);

    This can significantly increase the timeout length. I think you should
    instead use time_before() to see how many jiffies have passed since
    the start.

    However, the real question is why the reset function gets called under
    a spinlock in the first place. Can you try to rearrange the code so
    it doesn't need the lock at all and you can just use msleep() instead?

    Arnd

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