linux-kernel - Re: Watchdog reset trigger for eMMC

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Date:	Mon, 02 May 2016 08:27:38 +0200
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	Anand Moon <linux.amoon@...il.com>,
	Krzysztof Kozłowski <k.kozlowski@...sung.com>,
	Javier Martinez Canillas <javier@....samsung.com>
Cc:	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Watchdog reset trigger for eMMC

Hi Anand


On 2016-04-30 08:06, Anand Moon wrote:
> Hi All,
>
> Using microSD card when I try to write into /dev/watchdog device
> it triggers reboot of the board after timer expires.
> -----------------------------------------------------------------------------------------------
> root@...oidxu4l:~# echo 3 > /dev/watchdog
> [ 1659.021844] watchdog: watchdog0: watchdog did not stop!
> root@...oidxu4l:~#
> root@...oidxu4l:~#
> root@...oidxu4l:~#
> root@...oidxu4l:~#
> root@...oidxu4l:~#
>
> U-Boot 2016.03-00665-g563d8d9-dirty (Apr 04 2016 - 22:27:07 +0930) for
> ODROID-XU
>                  3
>
> CPU:   Exynos5422 @ 800 MHz
> Model: Odroid XU3 based on EXYNOS5422
> Board: Odroid XU3 based on EXYNOS5422
> Type:  xu4
> DRAM:  2 GiB
> -----------------------------------------------------------------------------------------------
> But when I try this on eMMC it just freezes.
> I know we have to set and unset gpio pin (SD_0.RST) to trigger reset
> before reboot.
> -----------------------------------------------------------------------------------------------
> root@...oidxu4e:~# echo 4 > /dev/watchdog
> [  639.192617] [c3] watchdog watchdog0: watchdog did not stop!
> root@...oidxu4e:~#
> root@...oidxu4e:~#
> root@...oidxu4e:~#
> -----------------------------------------------------------------------------------------------
> I would like to know what is way board reset after watchdog reset after timeout.

In my opinion hw watchdog reset is non-functional on Odroid U3/XU3/XU4 
boards due to
hardware design (eMMC reset line triggered from software). I see no way 
to workaround
this issue in the software.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland