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Sender: Guenter Roeck <groeck7@gmail.com>
Subject: Re: [PATCH v1 0/2] Watchdog Core Global Parameters
To:     Jerry Hoemann <jerry.hoemann@hpe.com>
Cc:     Flavio Suligoi <f.suligoi@asem.it>,
        "linux-watchdog@vger.kernel.org" <linux-watchdog@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        Mika Westerberg <mika.westerberg@linux.intel.com>
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From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <96a752d7-2818-70a5-ef69-0322f6b9bc42@roeck-us.net>
Date:   Tue, 9 Mar 2021 12:49:25 -0800
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On 3/9/21 10:42 AM, Jerry Hoemann wrote:
> On Tue, Mar 09, 2021 at 07:22:28AM -0800, Guenter Roeck wrote:
>> On 3/9/21 2:26 AM, Flavio Suligoi wrote:
>>> Hi Guenter,
>>>
>>>>> Instead of adding this kind of module parameters independently to each
>>>>> driver, the best solution is declaring each feature only once, in the
>>>>> watchdog core.
>>>>>
>>>>
>>>> I agree to and like the idea, but I don't see the point of letting drivers opt in
>>>> or opt out. This adds a lot of complexity for little if any gain.
>>>
>>> Do you mean that all the support for this "global parameters" should be done
>>> in the watchdog-core only, without write any code in each single
>>> "hardware" driver?
>>
>> Correct. It should not be up to the driver author to decide if they
>> want to opt out from global parameters or not. It should be up to
>> users, and users can opt out by not providing the parameters.
> 
> 
> Guenter,
> 
> What about parameters like "pretimeout"  that only some WD drivers have
> hw to support?
> 

Those drivers are supposed to set WDIOF_PRETIMEOUT. If they don't, any associated
module parameter would be ignored. That is quite similar to any other non-existing
module parameter.

> Might be nice to centralize these parameters as well, but leaving it up
> to users to decide might not make sense.
> 

Decide what, exactly ? Users can still provide a pretimeout module
parameter even if pretimeout is not supported for a given watchdog.
That is the case today, and it won't change.

Given that, I must admit that I don't really understand your concern.

> Or do you see the recent work to allow for a software pretimeout
> mechanism covering this?
>

That is completely orthogonal.

Guenter

> thanks
> 
> Jerry
> 
>>
>> Guenter
>>
>>>>
>>>> Guenter
>>>
>>> Regards,
>>>
>>> Flavio
>>>
>>>>
>>>>> Additionally, I added a implementation example of this "global"
>>>>> parameters using the module "wdat_wdt"
>>>>>
>>>>> In details:
>>>>>
>>>>> ===============================
>>>>> Watchdog Core Global Parameters
>>>>> ===============================
>>>>>
>>>>> Information for watchdog kernel modules developers.
>>>>>
>>>>> Introduction
>>>>> ============
>>>>>
>>>>> Different watchdog modules frequently require the same type of
>>>>> parameters (for example: *timeout*, *nowayout* feature,
>>>>> *start_enabled* to start the watchdog on module insertion, etc.).
>>>>> Instead of adding this kind of module parameters independently to each
>>>>> driver, the best solution is declaring each feature only once, in the
>>>>> watchdog core.
>>>>>
>>>>> In this way, each driver can read these "global" parameters and then,
>>>>> if needed, can implement them, according to the particular hw watchdog
>>>>> characteristic.
>>>>>
>>>>> Using this approach, it is possible reduce some duplicate code in the
>>>>> *new* watchdog drivers and simplify the code maintenance.  Moreover,
>>>>> the code will be clearer, since the same kind of parameters are often
>>>>> called with different names (see Documentation/watchdog/watchdog-
>>>> parameters.rst).
>>>>> Obviously, for compatibility reasons, we cannot remove the already
>>>>> existing parameters from the code of the various watchdog modules, but
>>>>> we can use this "global" approach for the new watchdog drivers.
>>>>>
>>>>>
>>>>> Global parameters declaration
>>>>> ==============================
>>>>>
>>>>> The global parameters data structure is declared in
>>>>> include/linux/watchdog.h, as::
>>>>>
>>>>> 	struct watchdog_global_parameters_struct {
>>>>> 		int timeout;
>>>>> 		int ioport;
>>>>> 		int irq;
>>>>> 		unsigned long features;
>>>>> 		/* Bit numbers for features flags */
>>>>> 		#define WDOG_GLOBAL_PARAM_VERBOSE	0
>>>>> 		#define WDOG_GLOBAL_PARAM_TEST_MODE	1
>>>>> 		#define WDOG_GLOBAL_PARAM_START_ENABLED	2
>>>>> 		#define WDOG_GLOBAL_PARAM_NOWAYOUT	3
>>>>> 	};
>>>>>
>>>>> The variable "feature" is a bitwise flags container, to store boolean
>>>>> features, such as:
>>>>>
>>>>> * nowayout
>>>>> * start_enable
>>>>> * etc...
>>>>>
>>>>> Other variables can be added, to store some numerical values and other
>>>>> data required.
>>>>>
>>>>> The global parameters are declared (as usual for the module
>>>>> parameters) in the first part of drivers/watchdog/watchdog_core.c file.
>>>>> The above global data structure is then managed by the function *void
>>>>> global_parameters_init()*, in the same file.
>>>>>
>>>>> Global parameters use
>>>>> =====================
>>>>>
>>>>> Each watchdog driver, to check if one of the global parameters is
>>>>> enabled, can use the corresponding in-line function declared in
>>>>> include/linux/watchdog.h.
>>>>> At the moment the following functions are ready to use:
>>>>>
>>>>> * watchdog_global_param_verbose_enabled()
>>>>> * watchdog_global_param_test_mode_enabled()
>>>>> * watchdog_global_param_start_enabled()
>>>>> * watchdog_global_param_nowayout_enabled()
>>>>>
>>>>>
>>>>>
>>>>> Flavio Suligoi (2):
>>>>>   watchdog: add global watchdog kernel module parameters structure
>>>>>   watchdog: wdat: add start_enable global parameter
>>>>>
>>>>>  Documentation/watchdog/index.rst              |  1 +
>>>>>  .../watchdog-core-global-parameters.rst       | 74 +++++++++++++++++++
>>>>>  drivers/watchdog/watchdog_core.c              | 74 +++++++++++++++++++
>>>>>  drivers/watchdog/wdat_wdt.c                   |  2 +
>>>>>  include/linux/watchdog.h                      | 42 +++++++++++
>>>>>  5 files changed, 193 insertions(+)
>>>>>  create mode 100644
>>>>> Documentation/watchdog/watchdog-core-global-parameters.rst
>>>>>
>>>
>