Messages in this thread | | | Subject | Re: [PATCH 2/4] alarmtimer: Make alarmtimer platform device child of RTC device | From | Stephen Boyd <> | Date | Thu, 16 Jan 2020 17:25:19 -0800 |
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Quoting Doug Anderson (2020-01-15 11:22:26) > Hi, > > On Wed, Jan 15, 2020 at 2:07 AM Thomas Gleixner <tglx@linutronix.de> wrote: > > > > Doug Anderson <dianders@chromium.org> writes: > > > On Thu, Jan 9, 2020 at 7:59 AM Stephen Boyd <swboyd@chromium.org> wrote: > > >> diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c > > >> index 4b11f0309eee..ccb6aea4f1d4 100644 > > >> --- a/kernel/time/alarmtimer.c > > >> +++ b/kernel/time/alarmtimer.c > > >> @@ -88,6 +88,7 @@ static int alarmtimer_rtc_add_device(struct device *dev, > > >> unsigned long flags; > > >> struct rtc_device *rtc = to_rtc_device(dev); > > >> struct wakeup_source *__ws; > > >> + struct platform_device *pdev; > > >> int ret = 0; > > >> > > >> if (rtcdev) > > >> @@ -99,6 +100,7 @@ static int alarmtimer_rtc_add_device(struct device *dev, > > >> return -1; > > >> > > >> __ws = wakeup_source_register(dev, "alarmtimer"); > > >> + pdev = platform_device_register_data(dev, "alarmtimer", -1, NULL, 0); > > > > > > Don't you need to check for an error here? If pdev is an error you'll > > > continue on your merry way. Before your patch if you got an error > > > registering the device it would have caused probe to fail. > > > > Yes, that return value should be checked > > > > > I guess you'd only want it to be an error if "rtcdev" is NULL? > > > > If rtcdev is not NULL then this code is not reached. See the begin of > > this function :) > > Wow, not sure how I missed that. I guess the one at the top of the > function is an optimization, though? It's being accessed without the > spinlock which means that it's not necessarily reliable, right? I > guess once the rtcdev has been set then it is never unset, but it does > seem like if two threads could call alarmtimer_rtc_add_device() at the > same time then it's possible that we could end up calling > wakeup_source_register() for both of them. Did I understand that > correctly? If I did then maybe it deserves a comment?
It also looks like we call wakeup_source_register() and get lucky that they're both called alarmtimer but they don't conflict with each other in sysfs. Once we try to add a device named "alarmtimer" to the platform bus it is the only one that can be added. I'll have to make this autogenerate some number for the device instead of using -1 as the id so that we don't see device name conflicts on the same bus.
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