linux-kernel - Re: [PATCH 3/5] watchdog: sp805: set WDOG_HW

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Date:   Wed, 23 May 2018 09:29:23 -0700
From:   Ray Jui <ray.jui@...adcom.com>
To:     Robin Murphy <robin.murphy@....com>,
        Scott Branden <scott.branden@...adcom.com>,
        Guenter Roeck <linux@...ck-us.net>
Cc:     Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
        linux-watchdog@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        bcm-kernel-feedback-list@...adcom.com,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Frank Rowand <frowand.list@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/5] watchdog: sp805: set WDOG_HW_RUNNING when appropriate

Hi Robin,

On 5/23/2018 4:48 AM, Robin Murphy wrote:
> On 23/05/18 08:52, Scott Branden wrote:
>>
>>
>> On 18-05-22 04:24 PM, Ray Jui wrote:
>>> Hi Guenter,
>>>
>>> On 5/22/2018 1:54 PM, Guenter Roeck wrote:
>>>> On Tue, May 22, 2018 at 11:47:18AM -0700, Ray Jui wrote:
>>>>> If the watchdog hardware is already enabled during the boot process,
>>>>> when the Linux watchdog driver loads, it should reset the watchdog and
>>>>> tell the watchdog framework. As a result, ping can be generated from
>>>>> the watchdog framework, until the userspace watchdog daemon takes over
>>>>> control
>>>>>
>>>>> Signed-off-by: Ray Jui <ray.jui@...adcom.com>
>>>>> Reviewed-by: Vladimir Olovyannikov 
>>>>> <vladimir.olovyannikov@...adcom.com>
>>>>> Reviewed-by: Scott Branden <scott.branden@...adcom.com>
>>>>> ---
>>>>>   drivers/watchdog/sp805_wdt.c | 22 ++++++++++++++++++++++
>>>>>   1 file changed, 22 insertions(+)
>>>>>
>>>>> diff --git a/drivers/watchdog/sp805_wdt.c 
>>>>> b/drivers/watchdog/sp805_wdt.c
>>>>> index 1484609..408ffbe 100644
>>>>> --- a/drivers/watchdog/sp805_wdt.c
>>>>> +++ b/drivers/watchdog/sp805_wdt.c
>>>>> @@ -42,6 +42,7 @@
>>>>>       /* control register masks */
>>>>>       #define    INT_ENABLE    (1 << 0)
>>>>>       #define    RESET_ENABLE    (1 << 1)
>>>>> +    #define    ENABLE_MASK    (INT_ENABLE | RESET_ENABLE)
>>>>>   #define WDTINTCLR        0x00C
>>>>>   #define WDTRIS            0x010
>>>>>   #define WDTMIS            0x014
>>>>> @@ -74,6 +75,18 @@ module_param(nowayout, bool, 0);
>>>>>   MODULE_PARM_DESC(nowayout,
>>>>>           "Set to 1 to keep watchdog running after device release");
>>>>>   +/* returns true if wdt is running; otherwise returns false */
>>>>> +static bool wdt_is_running(struct watchdog_device *wdd)
>>>>> +{
>>>>> +    struct sp805_wdt *wdt = watchdog_get_drvdata(wdd);
>>>>> +
>>>>> +    if ((readl_relaxed(wdt->base + WDTCONTROL) & ENABLE_MASK) ==
>>>>> +        ENABLE_MASK)
>>>>> +        return true;
>>>>> +    else
>>>>> +        return false;
>>>>
>>>>     return !!(readl_relaxed(wdt->base + WDTCONTROL) & ENABLE_MASK));
>>>>
>>>
>>> Note ENABLE_MASK contains two bits (INT_ENABLE and RESET_ENABLE); 
>>> therefore, a simple !!(expression) would not work? That is, the 
>>> masked result needs to be compared against the mask again to ensure 
>>> both bits are set, right?
>> Ray - your original code looks correct to me.  Easier to read and less 
>> prone to errors as shown in the attempted translation to a single 
>> statement.
> 
>      if (<boolean condition>)
>          return true;
>      else
>          return false;
> 
> still looks really dumb, though, and IMO is actually harder to read than 
> just "return <boolean condition>;" because it forces you to stop and 
> double-check that the logic is, in fact, only doing the obvious thing.

If you can propose a way to modify my original code above to make it 
more readable, I'm fine to make the change.

As I mentioned, I don't think the following change proposed by Guenter 
will work due to the reason I pointed out:

return !!(readl_relaxed(wdt->base + WDTCONTROL) & ENABLE_MASK));

> 
> Robin.
> 
> 
> 
> p.s. No thanks for making me remember the mind-boggling horror of 
> briefly maintaining part of this legacy codebase... :P
> 
> $ grep -r '? true : false' --include=*.cpp . | wc -l
> 951