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

From: Guenter Roeck
Date: Sat Apr 30 2016 - 20:05:00 EST


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@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!


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

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[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