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    SubjectRe: [PATCH 1/1]mmc: fix division by zero when calculate mmc erase time
    * Dong, Chuanxiao <chuanxiao.dong@intel.com> [2011-02-24 20:09:59 +0800]:

    >
    >
    > > -----Original Message-----
    > > From: Marc Koschewski [mailto:marc@osknowledge.org]
    > > Sent: Thursday, February 24, 2011 7:38 PM
    > > To: Dong, Chuanxiao
    > > Cc: linux-mmc@vger.kernel.org; cjb@laptop.org; adrian.hunter@nokia.com;
    > > linus.walleij@linaro.org; linux-kernel@vger.kernel.org
    > > Subject: Re: [PATCH 1/1]mmc: fix division by zero when calculate mmc erase time
    > >
    > > Hi,
    > >
    > > * Chuanxiao Dong <chuanxiao.dong@intel.com> [2011-02-24 19:18:01 +0800]:
    > >
    > > > Since if clock gating feature is enabled, the clock frequency may be zero when
    > > > host clock is gated. In such scenario, mmc_set_mmc_erase_timeout() may have a
    > > > division by zero bug.
    > > >
    > > > So this patch used mmc_host_clk_rate() to fix this.
    > > >
    > > > Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
    > > > ---
    > > > drivers/mmc/core/core.c | 10 ++++++++--
    > > > 1 files changed, 8 insertions(+), 2 deletions(-)
    > > >
    > > > diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
    > > > index 34a7e8c..12d0eb8 100644
    > > > --- a/drivers/mmc/core/core.c
    > > > +++ b/drivers/mmc/core/core.c
    > > > @@ -1201,8 +1201,14 @@ static void mmc_set_mmc_erase_timeout(struct
    > > mmc_card *card,
    > > > * less but not that much less, so fudge it by multiplying by 2.
    > > > */
    > > > timeout_clks <<= 1;
    > > > - timeout_us += (timeout_clks * 1000) /
    > > > - (card->host->ios.clock / 1000);
    > > > +
    > > > + /*
    > > > + * at this moment, host controller maybe clock gated, so make
    > > > + * sure we can get a correct host clock freq.
    > > > + */
    > > > + if (mmc_host_clk_rate(card->host))
    > > > + timeout_us += (timeout_clks * 1000) /
    > > > + (mmc_host_clk_rate(card->host) / 1000);
    > >
    > > Why don't you just reuse mmc_host_clk_rate()'s result instead of calling it twice?
    > This is a incline function and just return host->ios.clock. Reuse mmc_host_clk_rate()'s result need to add a new variable to save the value.

    It's not inline on trunk and it spinlocks.

    drivers/mmc/core/host.c:195

    194 */
    195 unsigned int mmc_host_clk_rate(struct mmc_host *host)
    196 {

    Cheers,
    Marc

    >
    > Thanks
    > Chuanxiao
    > --
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    >

    --
    Marc Koschewski


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