From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Lezcano Subject: Re: [PATCH v4] clocksource: arch_timer: Allow the device tree to specify uninitialized timer registers Date: Wed, 26 Nov 2014 12:51:08 +0100 Message-ID: <5475BEAC.9020208@linaro.org> References: <1412753627-28287-1-git-send-email-sonnyrao@chromium.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Doug Anderson Cc: "linux-arm-kernel@lists.infradead.org" , "devicetree@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Lorenzo Pieralisi , Olof Johansson , Thomas Gleixner , Will Deacon , Catalin Marinas , Sudeep Holla , Mark Rutland , Stephen Boyd , Marc Zyngier , Pawel Moll , Ian Campbell , Kumar Gala , Nathan Lynch , Rob Herring , Sonny Rao , =?UTF-8?B?SGVpa28gU3TDvGJuZXI=?= List-Id: devicetree@vger.kernel.org Hi Doug, Olof, IIUC, it sounds like this patch is needed from some other patches in=20 arm-soc. Olof was proposing to take this patch through its tree to=20 facilitate the integration. Olof, is it this patch you were worried about ? Thanks -- Daniel On 11/20/2014 12:01 AM, Doug Anderson wrote: > Daniel, > > On Wed, Oct 8, 2014 at 12:33 AM, Sonny Rao wr= ote: >> From: Doug Anderson >> >> Some 32-bit (ARMv7) systems are architected like this: >> >> * The firmware doesn't know and doesn't care about hypervisor mode a= nd >> 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 go= es >> down and comes back up it will get reinitialized to some other rando= m >> 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 goin= g >> to initialize the CNTVOFF registers when each CPU comes out of reset= =2E >> >> 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 bee= n >> 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 valu= e >> 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))" p= er >> Arnd Bergmann >> --- >> Documentation/devicetree/bindings/arm/arch_timer.txt | 8 ++++++++ >> drivers/clocksource/arm_arch_timer.c | 8 ++++++++ >> 2 files changed, 16 insertions(+) > > Do you know what the status of this patch is? This patch and Sonny's > patch at are needed on > Rockchip rk3288 for some specific things: > > 1. To make SMP happy with coreboot. > > 2. To (I assume) make SMP happy after S2R (no matter which firmware i= s > used since I don't think anyone has PSCI for rk3288). > > ...we still need a DTS entry atop these patches, but that's trivial t= o > add once these land. > > Thanks! > --=20 Linaro.org =E2=94=82 Open source software fo= r ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog