linux-kernel - Re: [PATCH] watchdog: dw

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Date:	Sun, 01 May 2016 17:30:26 +0100
From:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
CC:	Andy Shevchenko <andy.shevchenko@...il.com>,
	Wim Van Sebroeck <wim@...ana.be>,
	Haavard Skinnemoen <hskinnemoen@...il.com>,
	Hans-Christian Egtvedt <egtvedt@...fundet.no>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kernel-testers@...r.kernel.org, linux-watchdog@...r.kernel.org,
	Chris Mason <clm@...com>
Subject: Re: [PATCH] watchdog: dw_wdt: dont build for avr32

On Sunday 01 May 2016 03:09 PM, Guenter Roeck wrote:
> 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@...il.com> 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@...ck-us.net>
>>> 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@...il.com>
>>> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
>>> ---
>>>   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.

yes, i didn't get the time to monitor my build bot for last one week. 
But now that i go and see the results:
i386, m68k, mips allmodconfig failed with:
ERROR: "__udivdi3" [fs/btrfs/btrfs.ko] undefined!

regards
sudip