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Date:   Wed, 23 May 2018 11:09:20 -0700
From:   Guenter Roeck <linux@roeck-us.net>
To:     Robin Murphy <robin.murphy@arm.com>
Cc:     Ray Jui <ray.jui@broadcom.com>,
        Scott Branden <scott.branden@broadcom.com>,
        Mark Rutland <mark.rutland@arm.com>,
        devicetree@vger.kernel.org, linux-watchdog@vger.kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        linux-kernel@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
        bcm-kernel-feedback-list@broadcom.com,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        Frank Rowand <frowand.list@gmail.com>,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 3/5] watchdog: sp805: set WDOG_HW_RUNNING when appropriate
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On Wed, May 23, 2018 at 06:15:14PM +0100, Robin Murphy wrote:
> On 23/05/18 17:29, Ray Jui wrote:
> >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@broadcom.com>
> >>>>>>Reviewed-by: Vladimir Olovyannikov
> >>>>>><vladimir.olovyannikov@broadcom.com>
> >>>>>>Reviewed-by: Scott Branden <scott.branden@broadcom.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.
> 
> Well,
> 
> 	return readl_relaxed(wdt->base + WDTCONTROL) & ENABLE_MASK == ENABLE_MASK;
> 
> would probably be reasonable to anyone other than the 80-column zealots, but
> removing the silly boolean-to-boolean translation idiom really only
> emphasises the fact that it's fundamentally a big complex statement; for
> maximum clarity I'd be inclined to separate the two logical operations (read
> and comparison), e.g.:
> 
> 	u32 wdtcontrol = readl_relaxed(wdt->base + WDTCONTROL);
> 
> 	return wdtcontrol & ENABLE_MASK == ENABLE_MASK;

== has higher precendence than bitwise &, so this will need ( ),
but otherwise I agree.

> 
> which is still -3 lines vs. the original.
> 
> >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));
> 
> FWIW, getting the desired result should only need one logical not swapping
> for a bitwise one there:
> 
> 	return !(~readl_relaxed(wdt->base + WDTCONTROL) & ENABLE_MASK);
> 
> but that's well into "too clever for its own good" territory ;)

Yes, that would be confusing.

> 
> Robin.