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

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Date:	Sun, 1 May 2016 07:09:20 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
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 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.

Guenter