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

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Date:	Sat, 30 Apr 2016 17:04:40 -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 04/30/2016 11:38 AM, 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!
>

Pretty much what I suspected would happen. Oddly enough, the symbol was defined
in early avr32 patch sets [1], but dropped in the final commit after some
discussion [2]. Makes me wonder if the problem was always known.

Guenter

> 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
>
> regards
> sudip
>
---
[1] https://kldp.org/files/linux-2.6.16.11-avr32-20060626.patch_.txt
[2] http://fa.linux.kernel.narkive.com/4UhaxiM4/avr32-architecture-patch-against-linux-2-6-18-rc1-available