Re: [PATCH] watchdog: dw_wdt: dont build for avr32

[Guenter Roeck]

On 05/01/2016 02:04 AM, Sudip Mukherjee wrote:
> On Sunday 01 May 2016 02:13 AM, Guenter Roeck wrote:
> > On Sat, Apr 30, 2016 at 05:36:51PM -0700, Guenter Roeck wrote:
> > > On Sat, Apr 30, 2016 at 07:38:28PM +0100, Sudip Mukherjee wrote:
> > > > On Tue, Apr 12, 2016 at 11:01:28AM -0700, Guenter Roeck wrote:
> > > > > On Tue, Apr 12, 2016 at 05:58:20PM +0300, Andy Shevchenko wrote:
> > > > > > On Tue, Apr 12, 2016 at 4:39 PM, Sudip Mukherjee
> > > > > > <sudipm.mukherjee@xxxxxxxxx> wrote:
> > > > > > > On Tuesday 12 April 2016 06:36 PM, Guenter Roeck wrote:
> > > > > > > > On 04/11/2016 10:51 PM, Sudip Mukherjee wrote:
> > > > > > > > > The build of avr32 allmodconfig fails with the error:
> > > > > > > > > ERROR: "__avr32_udiv64" [drivers/watchdog/kempld_wdt.ko] undefined!
> > > > > > > > This means there is a direct 64 bit divide operation in the driver,
> > > > > > > > which we should identify and fix.
> > > > > >
> > > > > > This driver will quite likely never be used on AVR32. Do we need to
> > > > > > fix this due to some other architectures?
> > > > > >
> > > > > > > yes, there is.
> > > > > > >
> > > > > > > in function: kempld_wdt_set_stage_timeout()
> > > > > > > remainder = do_div(stage_timeout64, prescaler);
> > > > > >
> > > > > > > Any idea how to fix it?
> > > > > >
> > > > > > Not easy, however, prescaler value is ((1 << 21) - 1) which someone
> > > > > > might consider as (1 << 21) with lost in precision.
> > > > > >
> > > > > > Thus, shift on 20 bits right, add last bit to the value and shift on 1
> > > > > > bit right more.
> > > > > Sorry, I am missing something. do_div() should work fine with any 32 bit value
> > > > > as divisor, no matter what that value is. Why does it fail here ? And why does
> > > > > it work if I pass 0x1fffff as second parameter to do_div() directly ?
> > > >
> > > > Please let me know what i can do here to help solve the problem.
> > > > linux-next continues to fail for avr32, and to make matters worse we
> > > > also have the similar problem in btrfs.
> > > >
> > > > ERROR: "__avr32_udiv64" [fs/btrfs/btrfs.ko] undefined!
> > > > ERROR: "__avr32_udiv64" [drivers/watchdog/kempld_wdt.ko] undefined!
> > > >
> > > > Adding Chris to CC if he has some idea how to solve this error for btrfs.
> > > > Build log for next-20160429 is at:
> > > > https://travis-ci.org/sudipm-mukherjee/parport/jobs/126581065
> > >
> > > Try the patch below.
> > >
> > > Guenter
> > Sorry, patch wasn't complete.
> >
> > Guenter
> >
> > ---
> >  From c684f2cf54ecb256007288af23c24bfcdb2bbace Mon Sep 17 00:00:00 2001
> > From: Guenter Roeck <linux@xxxxxxxxxxxx>
> > Date: Sat, 30 Apr 2016 17:29:14 -0700
> > Subject: [PATCH] avr32: __div64_const32 is not ok
> >
> > Building avr32 images may fail with errors such as
> >
> > ERROR: "__avr32_udiv64" [fs/btrfs/btrfs.ko] undefined!
> > ERROR: "__avr32_udiv64" [drivers/watchdog/kempld_wdt.ko] undefined!
> >
> > gcc for avr32 generates those symbols for certain constants used
> > as divisor in do_div(). The problem can be avoided by setting
> > __div64_const32_is_OK to false for the architecture.
> >
> > Cc: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx>
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > ---
> >   arch/avr32/include/asm/Kbuild  | 1 -
> >   arch/avr32/include/asm/div64.h | 3 +++
> >   2 files changed, 3 insertions(+), 1 deletion(-)
> >   create mode 100644 arch/avr32/include/asm/div64.h
> >
> > diff --git a/arch/avr32/include/asm/Kbuild b/arch/avr32/include/asm/Kbuild
> > index 241b9b9729d8..d2be4688ac7b 100644
> > --- a/arch/avr32/include/asm/Kbuild
> > +++ b/arch/avr32/include/asm/Kbuild
> > @@ -3,7 +3,6 @@ generic-y += clkdev.h
> >   generic-y += cputime.h
> >   generic-y += delay.h
> >   generic-y += device.h
> > -generic-y += div64.h
> >   generic-y += emergency-restart.h
> >   generic-y += exec.h
> >   generic-y += futex.h
> > diff --git a/arch/avr32/include/asm/div64.h b/arch/avr32/include/asm/div64.h
> > new file mode 100644
> > index 000000000000..1f3328e178df
> > --- /dev/null
> > +++ b/arch/avr32/include/asm/div64.h
> > @@ -0,0 +1,3 @@
> > +#define __div64_const32_is_OK    false
> > +
> > +#include <asm-generic/div64.h>
>
> It looks like this patch has fixed about the error about the watchdog but for some reason I am still getting the error about the btrfs.
>
> ERROR: "__avr32_udiv64" [fs/btrfs/btrfs.ko] undefined!

Are you sure that this failure is limited to avr32 ?

Bisect for that problem points to commit "Btrfs: fix divide error upon chunk's stripe_len",
which modified stripe_len in struct map_lookup to 64 bit. map->stripe_length is used
at least once in a 64-bit divide operation, so I would expect to see more build failures.

A quick check shows that i386:allmodconfig now fails to build as well due to a 64-bit
divide operation in brtfs.

Guenter