Hi Richard, > -----Original Message----- > From: Richard Cochran <richardcoch...@gmail.com> > Sent: Sunday, May 24, 2020 10:11 AM > To: Jianyong Wu <jianyong...@arm.com> > Cc: net...@vger.kernel.org; yangbo...@nxp.com; john.stu...@linaro.org; > t...@linutronix.de; pbonz...@redhat.com; sean.j.christopher...@intel.com; > m...@kernel.org; Mark Rutland <mark.rutl...@arm.com>; w...@kernel.org; > Suzuki Poulose <suzuki.poul...@arm.com>; Steven Price > <steven.pr...@arm.com>; linux-kernel@vger.kernel.org; linux-arm- > ker...@lists.infradead.org; kvm...@lists.cs.columbia.edu; > k...@vger.kernel.org; Steve Capper <steve.cap...@arm.com>; Kaly Xin > <kaly....@arm.com>; Justin He <justin...@arm.com>; Wei Chen > <wei.c...@arm.com>; nd <n...@arm.com> > Subject: Re: [RFC PATCH v12 10/11] arm64: add mechanism to let user choose > which counter to return > > On Fri, May 22, 2020 at 04:37:23PM +0800, Jianyong Wu wrote: > > In general, vm inside will use virtual counter compered with host use > > phyical counter. But in some special scenarios, like nested > > virtualization, phyical counter maybe used by vm. A interface added in > > ptp_kvm driver to offer a mechanism to let user choose which counter > > should be return from host. > > Sounds like you have two time sources, one for normal guest, and one for > nested. Why not simply offer the correct one to user space automatically? If > that cannot be done, then just offer two PHC devices with descriptive names. >
It's a good idea, but in most case physical counter will not be used, so it's better not keep 2 ptp devices all the time. How about adding an extra argument in struct ptp_clock_info to serve as a flag, then we can control this flag using IOCTL to determine the counter type. In this way, no extra arguments needed in .getcrosststamp. But we also need specific code in ptp_ioctl to implement it like in this patch. The second way, maybe we can use the flag as a module parameter, this is easier to implement. @m...@kernel.org WDYT? > > diff --git a/drivers/ptp/ptp_chardev.c b/drivers/ptp/ptp_chardev.c > > index fef72f29f3c8..8b0a7b328bcd 100644 > > --- a/drivers/ptp/ptp_chardev.c > > +++ b/drivers/ptp/ptp_chardev.c > > @@ -123,6 +123,9 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int > cmd, unsigned long arg) > > struct timespec64 ts; > > int enable, err = 0; > > > > +#ifdef CONFIG_ARM64 > > + static long flag; > > static? This is not going to fly. Need remove here. > > > + * In most cases, we just need virtual counter from host and > > + * there is limited scenario using this to get physical counter > > + * in guest. > > + * Be careful to use this as there is no way to set it back > > + * unless you reinstall the module. > > How on earth is the user supposed to know this? > Yeah, It's odd , should be removed. > From your description, this "flag" really should be a module parameter. Maybe use flag as a module parameter is a better way. Thanks Jianyong > > Thanks, > Richard
