Messages in this thread | | | Date | Thu, 13 Dec 2012 21:10:24 -0700 | From | Jason Gunthorpe <> | Subject | Re: [PATCH 1/3] timekeeping: Add persistent_clock_exist flag |
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On Fri, Dec 14, 2012 at 11:13:30AM +0800, Feng Tang wrote:
> > This seems like a great use of that hardware resource, and no doubt > > those mach's also have a class RTC driver available talking to > > different hardware. > > Interesting to know this, thanks for the info. For the x86 desktop > and mobile processors I've used, the read_persistent_clock and rtc > are the same on-board device (always power on), so I see many time > related code are execuated twice, like init/suspend/resume if > HCTOSYS config is enabled, that's why I came up with the patches.
Ah, I see, there is some duplication here, my earlier comments about update_persistent_clock are not quite right, some places like PCs stick a RTC driver and then continue to access the same hardware directly outside the rtc driver context! That seems ugly :|
I see the PC CMOS rtc driver does not implement the set_mmss operation, instead running that code through update_persistent_clock.. That seems like a cleanup waiting to happen.
Regarding your problem - IMHO, it would be fantastic if the class RTC driver could be used instead of read_persistent_clock on PC.
John mentioned that read_persistent_clock had a requirement to work with IRQs off - that seems like it would be easy to incorporate into class rtc - for hardware that supports it (and PC is not the only RTC HW that can do this) Is that the only reason it still exists on pc?
I have to feel the long term direction should be to remove *_persistent_clock in favor of class RTC?
> > Maybe Feng would be better off adjusting read_persistent_clock to > > return ENODEV in such cases?? > > For mach's without read_persistent_clock capability, there is already > a weakly defined
This is used for arch's without the functionality, mach's are arch specific things. ARM provides a function pointer indirection for it's read_persistent_clock implementation.
Jason
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