From: will.deacon@arm•com (Will Deacon)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC PATCH 1/2] ARM/ARM64: arch_timer: Work around QorIQ Erratum A-008585
Date: Mon, 11 Apr 2016 10:19:13 +0100 [thread overview]
Message-ID: <20160411091913.GC15729@arm.com> (raw)
In-Reply-To: <1460341353-15619-2-git-send-email-oss@buserror.net>
On Sun, Apr 10, 2016 at 09:22:32PM -0500, Scott Wood wrote:
> Erratum A-008585 says that the ARM generic timer "has the potential to
> contain an erroneous value for a small number of core clock cycles
> every time the timer value changes" and that the workaround is to
> reread TVAL and count registers until successive reads return the same
> value.
>
> This erratum can be found on LS1021A (32-bit), LS1043A (64-bit), and
> LS2080A (64-bit).
>
> This patch is loosely based on work by Priyanka Jain and Bhupesh
> Sharma.
>
> Signed-off-by: Scott Wood <oss@buserror•net>
> ---
> .../devicetree/bindings/arm/arch_timer.txt | 4 ++
> arch/arm/boot/dts/ls1021a.dtsi | 1 +
> arch/arm/include/asm/arch_timer.h | 71 +++++++++++++++++++---
> arch/arm/include/asm/vdso_datapage.h | 1 +
> arch/arm/kernel/vdso.c | 1 +
> arch/arm/vdso/vgettimeofday.c | 2 +-
> arch/arm64/boot/dts/freescale/fsl-ls1043a.dtsi | 1 +
> arch/arm64/boot/dts/freescale/fsl-ls2080a.dtsi | 1 +
> arch/arm64/include/asm/arch_timer.h | 35 ++++++++---
> arch/arm64/include/asm/vdso_datapage.h | 1 +
> arch/arm64/kernel/asm-offsets.c | 1 +
> arch/arm64/kernel/vdso.c | 2 +
> arch/arm64/kernel/vdso/gettimeofday.S | 14 ++++-
> drivers/clocksource/arm_arch_timer.c | 5 ++
> 14 files changed, 121 insertions(+), 19 deletions(-)
[...]
> diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S
> index efa79e8..2e6008d 100644
> --- a/arch/arm64/kernel/vdso/gettimeofday.S
> +++ b/arch/arm64/kernel/vdso/gettimeofday.S
> @@ -207,7 +207,7 @@ ENDPROC(__kernel_clock_getres)
> /*
> * Read the current time from the architected counter.
> * Expects vdso_data to be initialised.
> - * Clobbers the temporary registers (x9 - x15).
> + * Clobbers the temporary registers (x9 - x17).
> * Returns:
> * - w9 = vDSO sequence counter
> * - (x10, x11) = (ts->tv_sec, shifted ts->tv_nsec)
> @@ -217,6 +217,7 @@ ENTRY(__do_get_tspec)
> .cfi_startproc
>
> /* Read from the vDSO data page. */
> + ldr w17, [vdso_data, #VDSO_TIMER_REREAD]
> ldr x10, [vdso_data, #VDSO_CS_CYCLE_LAST]
> ldp x13, x14, [vdso_data, #VDSO_XTIME_CLK_SEC]
> ldp w11, w12, [vdso_data, #VDSO_CS_MULT]
> @@ -225,6 +226,17 @@ ENTRY(__do_get_tspec)
> /* Read the virtual counter. */
> isb
> mrs x15, cntvct_el0
> + /*
> + * Erratum A-008585 requires back-to-back reads to be identical
> + * in order to avoid glitches.
> + */
> + cmp w17, #0
> + b.eq 2f
> +1: mrs x15, cntvct_el0
> + mrs x16, cntvct_el0
> + cmp x16, x15
> + b.ne 1b
> +2:
I'm not at all keen on having this in the vdso. Can you just force
use_syscall=1 instead, please?
Documentation/arm64/silicon-errata.txt needs updating too.
Will
next prev parent reply other threads:[~2016-04-11 9:19 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-11 2:22 [RFC PATCH 0/2] ARM/ARM64: arch_timer: QorIQ errata Scott Wood
2016-04-11 2:22 ` [RFC PATCH 1/2] ARM/ARM64: arch_timer: Work around QorIQ Erratum A-008585 Scott Wood
2016-04-11 9:19 ` Will Deacon [this message]
2016-04-11 9:52 ` Marc Zyngier
2016-04-12 5:48 ` Scott Wood
2016-04-12 9:07 ` Marc Zyngier
2016-04-13 5:41 ` Scott Wood
2016-04-13 7:36 ` Marc Zyngier
2016-04-13 13:22 ` Rob Herring
2016-04-17 0:58 ` Scott Wood
2016-04-11 2:22 ` [RFC PATCH 2/2] ARM64: arch_timer: Work around QorIQ Erratum A-009971 Scott Wood
2016-04-11 9:55 ` Marc Zyngier
2016-04-12 5:54 ` Scott Wood
2016-04-12 8:22 ` Marc Zyngier
2016-04-17 1:32 ` Scott Wood
2016-04-18 9:28 ` Marc Zyngier
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