On Sun, Sep 27, 2020 at 08:54:47AM -0700, Guenter Roeck wrote: > On 9/27/20 1:09 AM, Bruno Thomsen wrote: > > Den tor. 24. sep. 2020 kl. 12.53 skrev Uwe Kleine-König > > <u.kleine-koenig@xxxxxxxxxxxxxx>: > >> > >> Most boards using the pcf2127 chip (in my bubble) don't make use of the > >> watchdog functionality and the respective output is not connected. The > >> effect on such a board is that there is a watchdog device provided that > >> doesn't work. > >> > >> So only register the watchdog if the device tree has a "has-watchdog" > >> property. > >> > >> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> > >> --- > >> drivers/rtc/rtc-pcf2127.c | 3 ++- > >> 1 file changed, 2 insertions(+), 1 deletion(-) > >> > >> diff --git a/drivers/rtc/rtc-pcf2127.c b/drivers/rtc/rtc-pcf2127.c > >> index 5b1f1949b5e5..8bd89d641578 100644 > >> --- a/drivers/rtc/rtc-pcf2127.c > >> +++ b/drivers/rtc/rtc-pcf2127.c > >> @@ -340,7 +340,8 @@ static int pcf2127_watchdog_init(struct device *dev, struct pcf2127 *pcf2127) > >> u32 wdd_timeout; > >> int ret; > >> > >> - if (!IS_ENABLED(CONFIG_WATCHDOG)) > >> + if (!IS_ENABLED(CONFIG_WATCHDOG) || > >> + !device_property_read_bool(dev, "has-watchdog")) > >> return 0; > > > > I don't think the compiler can remove the function if > > CONFIG_WATCHDOG is disabled due to the device tree > > value check. Maybe it can if split into 2 conditions. > > > > If the first part of the expression is always false, the second > part should not even be evaluated. This is wrong. For || the second expression isn't evaluated if the first evaluates to true (and the whole expression becomes true). This is the intended behaviour: If CONFIG_WATCHDOG is off, we don't need to check for the dt property and just skip the watchdog part. > Either case, the code now hard depends on the compiler optimizing the > code away. > > It calls devm_watchdog_register_device() which doesn't exist > if CONFIG_WATCHDOG is not enabled. I didn't know that this is safe, > and I would personally not want to rely on it, but we live and > learn. AFAICT this is save and used in other places in the kernel, too. This is one of the reasons why you cannot compile the kernel with -O0. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ |
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