linux-kernel - Re: [PATCH v10 5/5] Watchdog: ARM SBSA Generic Watchdog half timeout panic support

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Message-ID: <56B6422C.7070302@roeck-us.net>
Date:	Sat, 6 Feb 2016 10:57:48 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Fu Wei <fu.wei@...aro.org>
Cc:	Timur Tabi <timur@...eaurora.org>,
	Rob Herring <robh+dt@...nel.org>,
	Paweł Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	Jon Corbet <corbet@....net>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-watchdog@...r.kernel.org, linux-doc@...r.kernel.org,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Linaro ACPI Mailman List <linaro-acpi@...ts.linaro.org>,
	rruigrok@...eaurora.org, "Abdulhamid, Harb" <harba@...eaurora.org>,
	Christopher Covington <cov@...eaurora.org>,
	Dave Young <dyoung@...hat.com>,
	Pratyush Anand <panand@...hat.com>,
	G Gregory <graeme.gregory@...aro.org>,
	Al Stone <al.stone@...aro.org>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Jon Masters <jcm@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	Leo Duran <leo.duran@....com>,
	Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH v10 5/5] Watchdog: ARM SBSA Generic Watchdog half timeout
 panic support

On 02/06/2016 10:02 AM, Fu Wei wrote:
> Hi Guenter,
>
> On 6 February 2016 at 07:54, Guenter Roeck <linux@...ck-us.net> wrote:
>> On 02/05/2016 10:21 AM, Fu Wei wrote:
>>>
>>> On 5 February 2016 at 22:42, Guenter Roeck <linux@...ck-us.net> wrote:
>>>>
>>>> On 02/05/2016 01:51 AM, Fu Wei wrote:
>>>>>
>>>>>
>>>>> Hi Guenter,
>>>>>
>>>>> On 4 February 2016 at 13:17, Guenter Roeck <linux@...ck-us.net> wrote:
>>>>>>
>>>>>>
>>>>>> On 02/03/2016 03:00 PM, Fu Wei wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On 4 February 2016 at 02:45, Timur Tabi <timur@...eaurora.org> wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Fu Wei wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> As you know I have made the pre-timeout support patch, If people
>>>>>>>>> like
>>>>>>>>> it, i am happy to go on upstream it separately.
>>>>>>>>>
>>>>>>>>> If we want to use pre-timeout here, user only can use get_pretimeout
>>>>>>>>> and disable panic by setting pretimeout to 0
>>>>>>>>> but user can not really set pretimeout, because "pre-timeout  ==
>>>>>>>>> timeout / 2 (always)".
>>>>>>>>> if user want to change pretimeout, he/she has to set_time instead.
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Ok, I think patches 4 and 5 should be combined, and I think the
>>>>>>>> Kconfig
>>>>>>>> entry should be removed and just use panic_enabled.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Agreed.
>>>>>
>>>>>
>>>>>
>>>>> np, will do
>>>>>
>>>>>>>
>>>>>>>
>>>>>>> NP, will update this patchset like that ,  thanks :-)
>>>>>>>
>>>>>>
>>>>>> Also, if panic is enabled, the timeout needs to be adjusted accordingly
>>>>>> (to only panic after the entire timeout period has expired, not after
>>>>>> half of it). We can not panic the system after timeout / 2.
>>>>>
>>>>>
>>>>>
>>>>> OK, my thought is
>>>>>
>>>>> if panic is enabled :
>>>>> |--------WOR-------WS0--------WOR-------WS1
>>>>> |------timeout------(panic)------timeout-----reset
>>>>>
>>>>> if panic is disabled .
>>>>> |--------WOR-------WS0--------WOR-------WS1
>>>>> |---------------------timeout---------------------reset
>>>>>
>>>>>     panic_enabled only can be configured when module is loaded by module
>>>>> parameter
>>>>>
>>>>> But user should know that max_timeout(panic_enable) =
>>>>> max_timeout(panic_disable) / 2
>>>>>
>>>>
>>>> That means you'll have to update max_timeout accordingly.
>>>
>>>
>>> panic_enabled only can be configured when module is loaded, so we
>>> don't need to update it.
>>>
>>> max_timeout will only be set up in the init stage.
>>>
>>> Does it make sense ? :-)
>>>
>> Not sure I understand your problem or question.
>>
>> max_timeout will have to reflect the correct maximum timeout, under
>> all circumstances. It will have to be set to the correct value before
>> the watchdog driver is registered.
>
> yes, understood,  my thought is :
>
> in  static int sbsa_gwdt_probe(struct platform_device *pdev)
>
> if (action) {
>          wdd->min_timeout = 1;
>          wdd->max_timeout = U32_MAX / gwdt->clk;
> } else {
>          wdd->min_timeout = 2;
>          wdd->max_timeout = U32_MAX / gwdt->clk * 2;

Pretty much, though you would also have to adjust all calculations
using gwdt->clk, in both set_timeout() and get_timeout(). Wonder if
you could adjust gwdt->clk instead.

Does min_timeout really have to be 2 if panic is disabled ?
The only reason seems to be the calculation in sbsa_gwdt_set_timeout().

	writel(timeout / 2 * gwdt->clk, gwdt->control_base + SBSA_GWDT_WOR);

Maybe you could use something like

	writel(timeout * (gwdt->clk / 2), ...);

instead. Or, as mentioned above, adjust the value of gwdt->clk
to include the factor.

Thanks,
Guenter