From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yingjoe Chen Subject: Re: [PATCH v4] clocksource: arch_timer: Allow the device tree to specify uninitialized timer registers Date: Wed, 26 Nov 2014 22:41:33 +0800 Message-ID: <1417012893.12707.12.camel@mtksdaap41> References: <1412753627-28287-1-git-send-email-sonnyrao@chromium.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1412753627-28287-1-git-send-email-sonnyrao-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Sonny Rao Cc: "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , Mark Rutland , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Lorenzo Pieralisi , "pawel.moll-5wv7dgnIgG8@public.gmane.org" , "ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org" , Marc Zyngier , Catalin Marinas , Daniel Lezcano , Will Deacon , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org" , Doug Anderson , "galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org" , Sudeep Holla , Olof Johansson , Nathan Lynch , Thomas Gleixner , Stephen Boyd List-Id: devicetree@vger.kernel.org On Wed, 2014-10-08 at 15:33 +0800, Sonny Rao wrote: > From: Doug Anderson > > Some 32-bit (ARMv7) systems are architected like this: > > * The firmware doesn't know and doesn't care about hypervisor mode and > we don't want to add the complexity of hypervisor there. > > * The firmware isn't involved in SMP bringup or resume. > > * The ARCH timer come up with an uninitialized offset (CNTVOFF) > between the virtual and physical counters. Each core gets a > different random offset. > > * The device boots in "Secure SVC" mode. > > * Nothing has touched the reset value of CNTHCTL.PL1PCEN or > CNTHCTL.PL1PCTEN (both default to 1 at reset) > > On systems like the above, it doesn't make sense to use the virtual > counter. There's nobody managing the offset and each time a core goes > down and comes back up it will get reinitialized to some other random > value. > > This adds an optional property which can inform the kernel of this > situation, and firmware is free to remove the property if it is going > to initialize the CNTVOFF registers when each CPU comes out of reset. > > Currently, the best course of action in this case is to use the > physical timer, which is why it is important that CNTHCTL hasn't been > changed from its reset value and it's a reasonable assumption given > that the firmware has never entered HYP mode. > > Note that it's been said that on ARMv8 systems the firmware and > kernel really can't be architected as described above. That means > using the physical timer like this really only makes sense for ARMv7 > systems. > > Signed-off-by: Doug Anderson > Signed-off-by: Sonny Rao > Reviewed-by: Mark Rutland > --- > Changes in v2: > - Add "#ifdef CONFIG_ARM" as per Will Deacon > > Changes in v3: > - change property name to arm,cntvoff-not-fw-configured and specify > that the value of CNTHCTL.PL1PC(T)EN must still be the reset value > of 1 as per Mark Rutland > > Changes in v4: > - change property name to arm,cpu-registers-not-fw-configured and > specify that all cpu registers must have architected reset values > per Mark Rutland > - change from "#ifdef CONFIG_ARM" to "if (IS_ENABLED(CONFIG_ARM))" per > Arnd Bergmann > --- > Documentation/devicetree/bindings/arm/arch_timer.txt | 8 ++++++++ > drivers/clocksource/arm_arch_timer.c | 8 ++++++++ > 2 files changed, 16 insertions(+) > > diff --git a/Documentation/devicetree/bindings/arm/arch_timer.txt b/Documentation/devicetree/bindings/arm/arch_timer.txt > index 37b2caf..256b4d8 100644 > --- a/Documentation/devicetree/bindings/arm/arch_timer.txt > +++ b/Documentation/devicetree/bindings/arm/arch_timer.txt > @@ -22,6 +22,14 @@ to deliver its interrupts via SPIs. > - always-on : a boolean property. If present, the timer is powered through an > always-on power domain, therefore it never loses context. > > +** Optional properties: > + > +- arm,cpu-registers-not-fw-configured : Firmware does not initialize > + any of the generic timer CPU registers, which contain their > + architecturally-defined reset values. Only supported for 32-bit > + systems which follow the ARMv7 architected reset values. > + > + Hi, Sorry for the (very) late reply. I just realize today MT8135 need this and the other patch [1] to boot SMP correctly. I've applied both patches and they works fine. Thanks :) However, I'm not sure if we really need to add new property. arm_arch_timer driver will only use virtual timer when virtual PPI interrupt is provided, so the following patch to timer dtsi will also works. I think if the firmware doesn't support virtual timer, it make sense to not supply virtual interrupt. timer { compatible = "arm,armv7-timer"; interrupts = , - , - , - ; + ; clock-frequency = <13000000>; }; Joe.C [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/305436.html -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html