From mboxrd@z Thu Jan 1 00:00:00 1970 From: dingtianhong@huawei.com (Ding Tianhong) Date: Thu, 19 Jan 2017 20:18:31 +0800 Subject: [PATCH RESEND v8 1/4] arm64: arch_timer: Add device tree binding for hisilicon-161010101 erratum In-Reply-To: <20170119121008.GE11176@leverpostej> References: <1484826406-16348-1-git-send-email-dingtianhong@huawei.com> <1484826406-16348-2-git-send-email-dingtianhong@huawei.com> <20170119121008.GE11176@leverpostej> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 2017/1/19 20:10, Mark Rutland wrote: > On Thu, Jan 19, 2017 at 07:46:43PM +0800, Ding Tianhong wrote: >> This erratum describes a bug in logic outside the core, so MIDR can't be >> used to identify its presence, and reading an SoC-specific revision >> register from common arch timer code would be awkward. So, describe it >> in the device tree. >> >> Signed-off-by: Ding Tianhong >> Acked-by: Rob Herring >> --- >> Documentation/devicetree/bindings/arm/arch_timer.txt | 8 ++++++++ >> 1 file changed, 8 insertions(+) >> >> diff --git a/Documentation/devicetree/bindings/arm/arch_timer.txt b/Documentation/devicetree/bindings/arm/arch_timer.txt >> index ad440a2..9116934 100644 >> --- a/Documentation/devicetree/bindings/arm/arch_timer.txt >> +++ b/Documentation/devicetree/bindings/arm/arch_timer.txt >> @@ -31,6 +31,14 @@ to deliver its interrupts via SPIs. >> This also affects writes to the tval register, due to the implicit >> counter read. >> >> +- hisilicon,erratum-161010101 : A boolean property. Indicates the presence of >> + erratum 161010101, which says that reading the counter is unreliable unless >> + reading twice on the register and the value of the second read is larger >> + than the first by less than 32. If the verification is unsuccessful, then >> + discard the value of this read and repeat this procedure until the verification >> + is successful. This also affects writes to the tval register, due to the >> + implicit counter read. > > This describes the workaround, which shouldn't be necessary. > > My understanding (from the cover letter) is that reads of the > {virtual,physical} counters may return a value precisely 32 above the > true value. > > So it would be better to say: > > - hisilicon,erratum-161010101 : A boolean property. Indicates the > presence of Hisilicon erratum 161010101, which says that reading the > counters is unreliable in some cases, and reads may return a value 32 > beyond the correct value. This also affects writes to the tval > registers, due to the implicit counter read. > > Thanks, > Mark. Looks more accurate. Thanks. Ding > > . >