linux-kernel - Re: [PATCH v4 7/9] watchdog: max77620: add support for the max77714 variant

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Date:   Mon, 29 Nov 2021 13:56:04 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Luca Ceresoli <luca@...aceresoli.net>
Cc:     linux-kernel@...r.kernel.org, Lee Jones <lee.jones@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        devicetree@...r.kernel.org, linux-rtc@...r.kernel.org,
        linux-watchdog@...r.kernel.org,
        Chiwoong Byun <woong.byun@...sung.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v4 7/9] watchdog: max77620: add support for the max77714
 variant

On 11/29/21 1:24 PM, Luca Ceresoli wrote:
[ ... ]
>>>   
>>> +static const struct max77620_variant max77620_wdt_data = {
>>> +	.wdt_info = {
>>> +		.identity = "max77620-watchdog",
>>> +		.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE,
>>> +	},
>>
>> That does not have to be, and should not be, part of device specific data,
>> just because of the identity string.
> 
> Ok, no problem, will fix, but I have two questions.
> 
> First, what's the reason? Coding style or a functional difference?
> Usually const data is preferred to runtime assignment.
> 

wdt_info is not chip specific variant information as nothing but the identity
string is different, and there is no technical need for that difference.

> Second: it's not clear how you expect it to be done. Looking into the

I gave you three options to pick from.

> kernel it looks like almost all drivers set a constant string. I could
> find only one exception, f71808e_wdt:
> https://elixir.bootlin.com/linux/v5.16-rc3/source/drivers/watchdog/f71808e_wdt.c#L471
> 
>> Either keep the current identity string,
>> mark max77620_wdt_info as __ro_after_init and overwrite the identity string
>> there during probe
> 
> And also remove 'static' I guess. Hm, I don't love this, as above I tend
> to prefer static const when possible for file-scoped data.
> 

Where did I suggest to remove 'static', and what would be the benefit of making
the variable global ?

>> or add the structure to max77620_wdt and fill it out there.
> 
> Do you mean like the following, untested, kind-of-pseudocode?
> 
>   struct max77620_wdt {
>   	struct device			*dev;
>   	struct regmap			*rmap;
> 	const struct max77620_variant	*drv_data;
> +	struct watchdog_info		info;     /* not a pointer! */
>   	struct watchdog_device		wdt_dev;
>   };
> 
> and then, in probe:
> 
>     wdt->dev = dev;
>     wdt->drv_data = (const struct max77620_variant *)id->driver_data;
>     /* ... assign other wdt fields ... */
> +  strlcpy(wdt_dev->info.identity, id->name, \
> +          sizeof(wdt_dev->info.identity));
> +  wdt_dev->info.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | \
> +                          WDIOF_MAGICCLOSE;
> 
For example, yes.

> Finally, what about simply:
> 
>   static const struct max77620_variant max77620_wdt_data = {
> 	.wdt_info = {
> -		.identity = "max77620-watchdog",
> +		.identity = "max77xxx-watchdog",
> 		.options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | ...
> 	},
> 
> and always use that struct unconditionally? The max63xx_wdt.c driver
> seems to do that. Or, if this is an issue for backward compatibility (is
> it?), just leave max77620_wdt_data and the .identity field will always
> be "max77620-watchdog" even when using a MAX77714.

Also ok with me.

Guenter