linux-kernel - Re: [PATCH 1/1]mmc: fix division by zero when calculate mmc erase time

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Date:	Thu, 24 Feb 2011 13:22:35 +0100
From:	Marc Koschewski <marc@...nowledge.org>
To:	"Dong, Chuanxiao" <chuanxiao.dong@...el.com>
Cc:	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"cjb@...top.org" <cjb@...top.org>,
	"adrian.hunter@...ia.com" <adrian.hunter@...ia.com>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1]mmc: fix division by zero when calculate mmc erase
 time

* Dong, Chuanxiao <chuanxiao.dong@...el.com> [2011-02-24 20:09:59 +0800]:

> 
> 
> > -----Original Message-----
> > From: Marc Koschewski [mailto:marc@...nowledge.org]
> > Sent: Thursday, February 24, 2011 7:38 PM
> > To: Dong, Chuanxiao
> > Cc: linux-mmc@...r.kernel.org; cjb@...top.org; adrian.hunter@...ia.com;
> > linus.walleij@...aro.org; linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH 1/1]mmc: fix division by zero when calculate mmc erase time
> > 
> > Hi,
> > 
> > * Chuanxiao Dong <chuanxiao.dong@...el.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@...el.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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