From mboxrd@z Thu Jan 1 00:00:00 1970 From: stefano.stabellini@eu.citrix.com (Stefano Stabellini) Date: Tue, 10 Nov 2015 15:58:53 +0000 Subject: [PATCH v2 7/7] xen/arm: set the system time in Xen via the XENPF_settime64 hypercall In-Reply-To: <4039287.QS1nrAMb0E@wuerfel> References: <1447156675-7418-7-git-send-email-stefano.stabellini@eu.citrix.com> <4039287.QS1nrAMb0E@wuerfel> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, 10 Nov 2015, Arnd Bergmann wrote: > On Tuesday 10 November 2015 11:57:55 Stefano Stabellini wrote: > > + op.u.settime64.nsecs = now.tv_nsec; > > + op.u.settime64.system_time = arch_timer_read_counter() * (u64)NSEC_PER_SEC; > > + do_div(op.u.settime64.system_time, arch_timer_get_rate()); > > NSEC_PER_SEC is a large number, doesn't that multiplication overflow the > 64-bit system_time variable? It could be a concern, you are right. I think I can solve this issue and remove multiple do_divs by calculating nsec_per_tick at initialization time and use it here and in xen_read_wallclock. > > + printk("GTOD: Setting to %llu.%u at %llu\n", > > %llu.%09u > > so you get the leading zeroes. > > > + op.u.settime64.secs, > > + op.u.settime64.nsecs, > > + op.u.settime64.system_time); > > + (void)HYPERVISOR_platform_op(&op); > > Arnd >