linux-kernel - Re: [Linaro-acpi] [PATCH v2 6/7] Watchdog: introduce ARM SBSA watchdog driver

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Date:	Fri, 22 May 2015 17:24:01 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linaro-acpi@...ts.linaro.org
Cc:	Hanjun Guo <hanjun.guo@...aro.org>,
	Guenter Roeck <linux@...ck-us.net>, corbet@....net,
	devicetree@...r.kernel.org, linux-watchdog@...r.kernel.org,
	jcm@...hat.com, timur@...eaurora.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, wim@...ana.be,
	tekkamanninja@...il.com, vgandhi@...eaurora.org
Subject: Re: [Linaro-acpi] [PATCH v2 6/7] Watchdog: introduce ARM SBSA watchdog driver

On Friday 22 May 2015 23:18:21 Hanjun Guo wrote:
> On 2015年05月22日 23:01, Guenter Roeck wrote:
> > On Fri, May 22, 2015 at 04:55:04PM +0200, Arnd Bergmann wrote:
> >> On Friday 22 May 2015 22:50:30 Hanjun Guo wrote:
> >>>> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> >>>> index e5e7c55..25a0df1 100644
> >>>> --- a/drivers/watchdog/Kconfig
> >>>> +++ b/drivers/watchdog/Kconfig
> >>>> @@ -152,6 +152,18 @@ config ARM_SP805_WATCHDOG
> >>>>          ARM Primecell SP805 Watchdog timer. This will reboot your system when
> >>>>          the timeout is reached.
> >>>>
> >>>> +config ARM_SBSA_WATCHDOG
> >>>> +     tristate "ARM SBSA Generic Watchdog"
> >>>> +     depends on ARM || ARM64 || COMPILE_TEST
> >>>
> >>> SBSA is for ARMv8-A based (64-bit) servers, no need to depends on ARM,
> >>> and why we depends on COMPILE_TEST?
> >>>
> >>
> >> I think it's a reasonable assumption that someone will sooner or later
> >> put that hardware into an ARM32 machine, or run a 32-bit kernel on
> >> a chip that has it.
> >>
> >> While SBSA requires this watchdog device, nothing prevents SoC
> >> manufacturers from using the same design in something that is not
> >> a server.
> 
>  From this point of view, I agree that SBSA watchdog design may used
> in other ARM SoCs in the future, but how about add it back when this
> kind of hardware showing up?

If it builds on ARM32, I'd rather leave the option in, it doesn't hurt.

> > Tricky, though. Since teh driver uses arm specific clock functions,
> > I don't think this can compile on a non-arm machine.
> 
> Since it depends on ARM64/ARM, we can temporary release from that now 

We have to drop the '|| COMPILE_TEST' though as a result, or fix the
driver to look up the clock in DT and call 'clk_get_rate'.

That will break the ACPI case, but ACPI could use platform_data to
pass the clock rate into the driver, to make it independent of
low-level APIs.

	Arnd
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