linux-kernel - Re: [PATCH 2/2 v3] mmc: dw_mmc: Fix the CTO overflow calculation for 32-bit systems

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Date:   Mon, 26 Feb 2018 15:14:21 +0000
From:   Evgeniy Didin <Evgeniy.Didin@...opsys.com>
To:     "andy.shevchenko@...il.com" <andy.shevchenko@...il.com>,
        "Evgeniy.Didin@...opsys.com" <Evgeniy.Didin@...opsys.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Alexey.Brodkin@...opsys.com" <Alexey.Brodkin@...opsys.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "dianders@...omium.org" <dianders@...omium.org>,
        "Vineet.Gupta1@...opsys.com" <Vineet.Gupta1@...opsys.com>,
        "Eugeniy.Paltsev@...opsys.com" <Eugeniy.Paltsev@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>
Subject: Re: [PATCH 2/2 v3] mmc: dw_mmc: Fix the CTO overflow calculation
 for 32-bit systems

On Mon, 2018-02-26 at 16:39 +0200, Andy Shevchenko wrote:
> On Mon, Feb 26, 2018 at 4:34 PM, Evgeniy Didin
> <Evgeniy.Didin@...opsys.com> wrote:
> > In commit 4c2357f57dd5 ("mmc: dw_mmc: Fix the CTO timeout calculation")
> > have been made changes which can cause multiply overflow for 32-bit systems.
> > The value of cto_ms is lower the drto_ms, but nevertheless overflow can occur.
> > Lets cast this multiply to u64 type which prevents overflow.
> > -       cto_ms = DIV_ROUND_UP(MSEC_PER_SEC * cto_clks * cto_div, host->bus_hz);
> > +
> > +       cto_ms = DIV_ROUND_UP((u64)MSEC_PER_SEC * cto_clks * cto_div, host->bus_hz);
> 
> IIRC, someone commented on this or similar, i.e.
> 
> DIV_ROUND_UP_ULL() ?
Switch DIV_ROUND_UP macro to DIV_ROUND_UP_ULL is not reasonable
because overflow happens on multiply and DIV_ROUND_UP_ULL helps
with sum overflow.

--
Best regards,
Evgeniy Didin