> -----Original Message----- > From: Marcelo Tosatti [mailto:mtosatti@xxxxxxxxxx] > Sent: Thursday, January 12, 2012 6:03 PM > To: Zhang, Yang Z > Cc: qemu-devel@xxxxxxxxxx; avi@xxxxxxxxxx; aliguori@xxxxxxxxxx; Zhang, > Xiantao; Shan, Haitao; kvm@xxxxxxxxxxxxxxx > Subject: Re: [PATCH 3/3] stop the periodic RTC update timer > > On Thu, Jan 12, 2012 at 07:59:06AM -0200, Marcelo Tosatti wrote: > > On Thu, Jan 12, 2012 at 12:00:06AM +0000, Zhang, Yang Z wrote: > > > > -----Original Message----- > > > > From: Marcelo Tosatti [mailto:mtosatti@xxxxxxxxxx] > > > > > > > > Regarding the UIP bit, a guest could read it in a loop and wait > > > > for the value to change. But you can emulate it in > > > > cmos_ioport_read by reading the host time, that is, return 1 > > > > during 244us, 0 for remaining of the second, and have that in sync with > update-cycle-ended interrupt if its enabled. > > > Yes. Guest may use the loop to read RTC, but the point is the guest is waiting > for the UIP changed to 0. If this bit always equal to 0 , guest will never go into the > loop. For real RTC, this may wrong, because the RTC cannot give you the valid > value during the update cycle. But the virtual RTC doesn't' need this logic, > whenever you read it, it will always return the right value to you. > > > > Can't it wait a change from 0 to 1? > > The point is the guest can use the hardware as it pleases, not only as is suggested > in the hardware documentation. You are right. I will add it to next version. best regards yang -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
