On Wed, Apr 12, 2023 at 12:02:04PM +0000, Li,Rongqing wrote: > > > > -----Original Message----- > > From: Sean Christopherson <seanjc@xxxxxxxxxx> > > Sent: Wednesday, February 8, 2023 11:04 PM > > To: Michael Kelley (LINUX) <mikelley@xxxxxxxxxxxxx> > > Cc: Li,Rongqing <lirongqing@xxxxxxxxx>; KY Srinivasan <kys@xxxxxxxxxxxxx>; > > Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>; wei.liu@xxxxxxxxxx; Dexuan Cui > > <decui@xxxxxxxxxxxxx>; tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; > > bp@xxxxxxxxx; dave.hansen@xxxxxxxxxxxxxxx; x86@xxxxxxxxxx; > > linux-hyperv@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx > > Subject: Re: [PATCH] clockevents/drivers/i8253: Do not zero timer counter in > > shutdown > > > > On Wed, Feb 08, 2023, Michael Kelley (LINUX) wrote: > > > From: lirongqing@xxxxxxxxx <lirongqing@xxxxxxxxx> Sent: Monday, > > > February 6, 2023 5:15 PM > > > > > > > > Zeroing the counter register in pit_shutdown() isn't actually > > > > supposed to stop it from counting, will causes the PIT to start > > > > running again, From the spec: > > > > > > > > The largest possible initial count is 0; this is equivalent to 216 for > > > > binary counting and 104 for BCD counting. > > > > > > > > The Counter does not stop when it reaches zero. In Modes 0, 1, 4, and 5 > > the > > > > Counter "wraps around" to the highest count, either FFFF hex for binary > > > > count- ing or 9999 for BCD counting, and continues counting. > > > > > > > > Mode 0 is typically used for event counting. After the Control Word is > > > > written, OUT is initially low, and will remain low until the Counter > > > > reaches zero. OUT then goes high and remains high until a new count or a > > > > new Mode 0 Control Word is written into the Counter. > > > > > > > > Hyper-V and KVM follow the spec, the issue that 35b69a42 > > > > "(clockevents/drivers/ > > > > i8253: Add support for PIT shutdown quirk") fixed is in i8253 > > > > drivers, not Hyper-v, so delete the zero timer counter register in > > > > shutdown, and delete PIT shutdown quirk for Hyper-v > > > > > > From the standpoint of Hyper-V, I'm good with this change. But > > > there's a risk that old hardware might not be compliant with the spec, > > > and needs the zero'ing for some reason. The experts in the x86 space > > > will be in the best position to assess the risk. > > > > Yep, my feeling exactly. My input is purely from reading those crusty old specs. > > > > Ping I guess you want Thomas Gleixner and Daniel Lezcano's attention. > > Thanks > > -Li
