linux-kernel - Re: [PATCH] MMC: core: cap MMC card timeouts at 2 seconds.

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Message-ID: <CAPDyKFrpXc7cODie9g-QK_ZhVpmVZPQ36TDF9CWJcVPL_-EU2Q@mail.gmail.com>
Date:	Thu, 31 May 2012 18:00:44 +0800
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	"Torne (Richard Coles)" <torne@...gle.com>
Cc:	cjb@...top.org, linus.walleij@...aro.org, jh80.chung@...sung.com,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	ben@...adent.org.uk
Subject: Re: [PATCH] MMC: core: cap MMC card timeouts at 2 seconds.

Hi Richard,

On 29 May 2012 17:02, Torne (Richard Coles) <torne@...gle.com> wrote:
> From: "Torne (Richard Coles)" <torne@...gle.com>
>
> MMC CSD info can specify very large, ridiculous timeouts, big enough to
> overflow timeout_ns on 32-bit machines. This can result in the card
> timing out on every operation because the wrapped timeout value is far
> too small.
>
> Fix the overflow by capping the result at 2 seconds.  Cards specifying
> longer timeouts are almost certainly insane, and host controllers
> generally cannot support timeouts that long in any case.
>
> 2 seconds should be plenty of time for any card to actually function;
> the timeout calculation code is already using 1 second as a "worst case"
> timeout for cards running in SPI mode.
>
> Signed-off-by: Torne (Richard Coles) <torne@...gle.com>
> ---
>  drivers/mmc/core/core.c |   11 ++++++++++-
>  1 files changed, 10 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 0b6141d..3b4a9fc 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -512,7 +512,16 @@ void mmc_set_data_timeout(struct mmc_data *data, const struct mmc_card *card)
>        if (data->flags & MMC_DATA_WRITE)
>                mult <<= card->csd.r2w_factor;
>
> -       data->timeout_ns = card->csd.tacc_ns * mult;
> +       /*
> +        * The timeout in nanoseconds may overflow with some cards. Cap it at
> +        * two seconds both to avoid the overflow and also because host
> +        * controllers cannot generally generate timeouts that long anyway.
> +        */
> +       if (card->csd.tacc_ns <= (2 * NSEC_PER_SEC) / mult)
> +               data->timeout_ns = card->csd.tacc_ns * mult;
> +       else
> +               data->timeout_ns = 2 * NSEC_PER_SEC;
> +

The above looks OK to me, although if doing this for tacc_ns we might
want to do this for tacc_clks as well. Could we include that is this
patch as well?

>        data->timeout_clks = card->csd.tacc_clks * mult;
>
>        /*
> --
> 1.7.7.3
>
> --
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Kind regards
Ulf Hansson
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