linux-kernel - Re: [PATCH 5/7] arm64: arch_timer: work around Hisilicon erratum 161010101

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Date:   Thu, 2 Feb 2017 20:21:13 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     catalin.marinas@....com, dingtianhong@...wei.com,
        will.deacon@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: Re: [PATCH 5/7] arm64: arch_timer: work around Hisilicon erratum
 161010101

On Tue, Jan 31, 2017 at 12:19:54PM +0000, Mark Rutland wrote:
> From: Ding Tianhong <dingtianhong@...wei.com>
> 
> Erratum Hisilicon-161010101 says that the ARM generic timer counter "has
> the potential to contain an erroneous value when the timer value
> changes". Accesses to TVAL (both read and write) are also affected due
> to the implicit counter read. Accesses to CVAL are not affected.
> 
> The workaround is to reread the system count registers until the value
> of the second read is larger than the first one by less than 32, the
> system counter can be guaranteed not to return wrong value twice by
> back-to-back read and the error value is always larger than the correct
> one by 32. Writes to TVAL are replaced with an equivalent write to CVAL.
> 
> Signed-off-by: Ding Tianhong <dingtianhong@...wei.com>
> [Mark: split patch, fix Kconfig, reword commit message]
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> ---

Acked-by: Daniel Lezcano <daniel.lezcano@...aro.org>