From: oss@buserror•net (Scott Wood)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v3 3/3] arm64: arch_timer: Work around QorIQ Erratum A-008585
Date: Thu, 07 Jul 2016 12:39:42 -0500 [thread overview]
Message-ID: <1467913182.32358.68.camel@buserror.net> (raw)
In-Reply-To: <577E524F.3030403@huawei.com>
On Thu, 2016-07-07 at 20:59 +0800, Ding Tianhong wrote:
> On 2016/7/7 19:51, Marc Zyngier wrote:
> >
> > On 07/07/16 12:37, Ding Tianhong wrote:
> > >
> > > On 2016/7/7 17:49, Marc Zyngier wrote:
> > > >
> > > > What makes you think that ignoring the two bottom bits is a safe thing
> > > > to do? Talking about performance when the HW has such a dramatic bug
> > > > is
> > > > like putting a bigger engine on a car that has no brakes: you just hit
> > > > the wall quicker.
> > > >
> > > > Thanks,
> > > >
> > > I have a chip which has the same problem like Scott's chip, and I
> > > wish to solve this problem in the same way, our chip designer told me
> > > that if you got a wrong value from the cntvct_el0, you would not get
> > > a wrong value until 8 cycles later, so I could ignoring the lowest 3
> > > bits if I reading twice together.
> > Is that CPU cycles? Or timer cycles? What guarantees do you have that
> > the two reads are *always* done in the right timing window?
> >
> The timer counter only use 56 bits in aarch64, my chip would change one of
> the higher?
> bit(55 to 3) to a wrong value when occur bug, so there will be more than 8
> cycles between
> correct value and wrong value from the timer counter. Maybe Scott's problem
> is not just like
> mine.
It's not like yours. ?Most errors I saw were time going backwards by 1, 3, or
7 cycles (with occasional larger errors).
-Scott
next prev parent reply other threads:[~2016-07-07 17:39 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-01 22:41 [PATCH v3 1/3] arm64: arch_timer: Add device tree binding for A-008585 erratum Scott Wood
2016-07-01 22:41 ` [PATCH v3 2/3] arm64: dts: Add timer erratum property for LS2080A and LS1043A Scott Wood
2016-07-01 22:41 ` [PATCH v3 3/3] arm64: arch_timer: Work around QorIQ Erratum A-008585 Scott Wood
2016-07-04 9:58 ` Will Deacon
2016-07-07 9:34 ` Ding Tianhong
2016-07-07 9:49 ` Marc Zyngier
2016-07-07 11:37 ` Ding Tianhong
2016-07-07 11:51 ` Marc Zyngier
2016-07-07 12:59 ` Ding Tianhong
2016-07-07 17:39 ` Scott Wood [this message]
2016-07-08 0:51 ` Ding Tianhong
2016-07-05 15:43 ` [PATCH v3 1/3] arm64: arch_timer: Add device tree binding for A-008585 erratum Rob Herring
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