Re: [PATCH 3/5] watchdog: sp805: set WDOG_HW_RUNNING when appropriate

From: Robin Murphy
Date: Wed May 23 2018 - 12:22:05 EST

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@xxxxxxxxxxxx>
Reviewed-by: Vladimir Olovyannikov <vladimir.olovyannikov@xxxxxxxxxxxx>
Reviewed-by: Scott Branden <scott.branden@xxxxxxxxxxxx>
---
 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 @@
ÂÂÂÂÂ /* control register masks */
ÂÂÂÂÂ #defineÂÂÂ INT_ENABLEÂÂÂ (1 << 0)
ÂÂÂÂÂ #defineÂÂÂ RESET_ENABLEÂÂÂ (1 << 1)
+ÂÂÂ #defineÂÂÂ ENABLE_MASKÂÂÂ (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,
ÂÂÂÂÂÂÂÂÂ "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)
+{
+ÂÂÂ struct sp805_wdt *wdt = watchdog_get_drvdata(wdd);
+
+ÂÂÂ if ((readl_relaxed(wdt->base + WDTCONTROL) & ENABLE_MASK) ==
+ÂÂÂÂÂÂÂ ENABLE_MASK)
+ÂÂÂÂÂÂÂ return true;
+ÂÂÂ else
+ÂÂÂÂÂÂÂ return false;

ÂÂÂÂreturn !!(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.

ÂÂÂÂÂif (<boolean condition>)
ÂÂÂÂÂÂÂÂ return true;
ÂÂÂÂÂelse
ÂÂÂÂÂÂÂÂ 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;

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 ;)

Robin.