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

[Evgeniy Didin]

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@xxxxxxxxxxxx> 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.
> > -ÂÂÂÂÂÂÂcto_ms = DIV_ROUND_UP(MSEC_PER_SEC * cto_clks * cto_div, host->bus_hz);
> > +
> > +ÂÂÂÂÂÂÂcto_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