From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jisheng.Zhang@synaptics.com (Jisheng Zhang) Date: Tue, 27 Feb 2018 11:52:43 +0800 Subject: [PATCH 2/2 v3] mmc: dw_mmc: Fix the CTO overflow calculation for 32-bit systems In-Reply-To: <1519676841.2997.7.camel@synopsys.com> References: <20180226143413.44134-1-Evgeniy.Didin@synopsys.com> <20180226143413.44134-3-Evgeniy.Didin@synopsys.com> <1519658060.31245.4.camel@synopsys.com> <1519665265.31245.6.camel@synopsys.com> <1519676841.2997.7.camel@synopsys.com> List-ID: Message-ID: <20180227115243.7ca84b3b@xhacker.debian> To: linux-snps-arc@lists.infradead.org On Mon, 26 Feb 2018 20:27:22 +0000 Alexey Brodkin wrote: > Hi Andy, > > On Mon, 2018-02-26@20:30 +0200, Andy Shevchenko wrote: > > On Mon, Feb 26, 2018 at 7:14 PM, Evgeniy Didin > > wrote: > > > On Mon, 2018-02-26 at 18:53 +0200, Andy Shevchenko wrote: > > > > On Mon, Feb 26, 2018 at 5:14 PM, Evgeniy Didin > > > > wrote: > > > > > On Mon, 2018-02-26 at 16:39 +0200, Andy Shevchenko wrote: > > > > > > On Mon, Feb 26, 2018 at 4:34 PM, Evgeniy Didin > > > > > > 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. > > > > > > > > Did you try to compile your code for 32-bit target? > > > > > > Yes, we have compiled code for 32-bit system. > > > I am wondering why are you asking that? > > > > Because I simple didn't believe you. > > Well world around us is much more complicated than it sometimes looks like :) > > > ERROR: "__udivdi3" [drivers/mmc/host/dw_mmc.ko] undefined! > > ...scripts/Makefile.modpost:92: recipe for target '__modpost' failed > > make[2]: *** [__modpost] Error 1 > > That's right __udivdi3() is not defined for some architectures but it is defined for > some others including ARC, Xtensa etc, see > https://elixir.bootlin.com/linux/latest/ident/__udivdi3 > > What happens __udivdi3() is implemented in libgcc in one form or another form > be it pure assembly or generic implementation written in C. > > So maybe we need to add export of __udivdi3() for other arches, what do you think? Per my understanding, Linux kernel prefer to make use of do_div or implementations in for 64bit divide Thanks