On Wed, 13 Aug 2025 12:35:31 +0100, Alexandru Elisei <alexandru.elisei@xxxxxxx> wrote: > > Hello, > > On Wed, Aug 13, 2025 at 11:55:48AM +0100, Sudeep Holla wrote: > > +Alexandru > > > > On Thu, Aug 07, 2025 at 05:02:39PM +0100, Marc Zyngier wrote: > > > For the past 10 years, both Mark and I have been lamenting about the > > > sorry state of the badly named "arch_timer" driver, and about the way > > > the MMIO part is intricately weaved into the system-register part. > > > > > > The time has finally come to have a stab at it. > > > > > > This small series simply creates a new timer driver for the MMIO arch > > > timer, and only that. It is an actual driver, and not some kludge that > > > has to run super early (that's what the per-CPU timers are for). This > > > allows, in turn, a pretty large cleanup of the per-CPU driver, though > > > there is more to come -- one thing at a time. > > > > > > As an added bonus, we get a clocksource, which the original code > > > didn't provide. Just in case it might be useful. The end-result is far > > > more readable, and about 100 lines smaller. > > > > > > > (Tested it on Juno R2 and FVP in both DT and ACPI boot) > > > > Tested-by: Sudeep Holla <sudeep.holla@xxxxxxx> > > Reviewed-by: Sudeep Holla <sudeep.holla@xxxxxxx> Thanks! > > > > Alexandru found it useful(avoids some unexpected hang IIUC) in his setup > > based on bootwrapper which doesn't initialise MMIO timers. > > Just FYI, this is the testing that I did. > > Without this series, if firmware (boot-wrapper-aarch64 in my testing) doesn't > configure access to the memory-mapped timer: > > [ 0.000000] arch_timer: Unable to find a suitable frame in timer @ 0x000000002a810000 > [ 0.000000] Failed to initialize '/timer@2a810000': -22 > .. > [ 0.528000] kvm [1]: kvm_arch_timer: uninitialized timecounter > .. Right, that's one of the many problems with the tight coupling between sysreg and MMIO timers -- if one fails, they both fail, and you're pretty lucky if you manage to limp along after that. > # ls /dev/kvm > ls: cannot access '/dev/kvm': No such file or directory > > With this series, if firmware doesn't configure access to the memory-mapped > timer: > > [ 0.549399] kvm [1]: Hyp nVHE mode initialized successfully > .. > [ 2.018050] arch-timer-mmio 2a810000.timer: Unable to find a suitable frame in timer @ 0x000000002a810000 > [ 2.018123] arch-timer-mmio 2a810000.timer: probe with driver arch-timer-mmio failed with error -22 Ah, you have managed to test the error path. Thanks for that! M. -- Without deviation from the norm, progress is not possible.
