From: Samuel Holland <samuel@sholland.org>
To: Daniel Lezcano <daniel.lezcano@linaro.org>,
Marc Zyngier <marc.zyngier@arm.com>,
Maxime Ripard <maxime.ripard@bootlin.com>,
Chen-Yu Tsai <wens@csie.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-sunxi@googlegroups.com,
Mark Rutland <Mark.Rutland@arm.com>
Subject: Re: [PATCH 0/2] Allwinner A64 timer workaround
Date: Wed, 11 Jul 2018 21:23:36 -0500 [thread overview]
Message-ID: <903c9e71-dde1-78d5-ed52-fcf47821918e@sholland.org> (raw)
In-Reply-To: <d72937af-cb46-27cf-809a-507ba5e47568@linaro.org>
On 07/04/18 03:41, Daniel Lezcano wrote:
> On 04/07/2018 10:16, Marc Zyngier wrote:
>> On 03/07/18 19:42, Samuel Holland wrote:
>>> On 07/03/18 10:09, Marc Zyngier wrote:
>>>> On 11/05/18 03:27, Samuel Holland wrote:
>>>>> Hello,
>>>>>
>>>>> Several people (including me) have experienced extremely large system
>>>>> clock jumps on their A64-based devices, apparently due to the architectural
>>>>> timer going backward, which is interpreted by Linux as the timer wrapping
>>>>> around after 2^56 cycles.
>>>>>
>>>>> Investigation led to discovery of some obvious problems with this SoC's
>>>>> architectural timer, and this patch series introduces what I believe is
>>>>> the simplest workaround. More details are in the commit message for patch
>>>>> 1. Patch 2 simply enables the workaround in the device tree.
>>>>
>>>> What's the deal with this series? There was a couple of nits to address, and
>>>> I was more or less expecting a v2.
>>>
>>> I got reports that people were still occasionally having clock jumps after
>>> applying this series, so I wanted to attempt a more complete fix, but I haven't
>>> had time to do any deeper investigation. I think this series is still beneficial
>>> even if it's not a complete solution, so I'll come back with another patch on
>>> top of this if/once I get it fully fixed.
>>>
>>> I'll prepare a v2 with a bounded loop. Presumably, 3 * (max CPU Hz) / (24MHz
>>> timer) ≈ 150 should be a conservative iteration limit?
>>
>> Should be OK.
>>
>> Maxime: How do you want to deal with the documentation aspect? We need
>> an erratum number, but AFAIU the concept hasn't made it into the silicom
>> vendor's brain yet. Any chance you could come up with something that
>> uniquely identifies this?
>
> I went through the different pointers provided in the description but I
> did not find a clear statement that is a hardware issue or may be I
> missed it.
>
> Are we sure there isn't another subsystem responsible on this
> instability ? (eg PM or something else)
This issue has been observed on kernels with and without DVFS, across several
Linux, U-Boot, and Trusted Firmware versions. It has not been observed on any
other Allwinner SoC, including the A64's twin, the H5.
In fact, this workaround was recently successfully used in U-Boot [1] to fix
issues with an MMC driver that needed reliable numbers from CNTVCT.
So while the vendor hasn't confirmed it (and I wouldn't count on that
happening), everything I've seen points to it being a silicon bug, not a
software issue.
[1]:
https://git.denx.de/?p=u-boot.git;a=commit;h=be0d217952222b2bd3ed071de9bb0c66d8cc80d9
>>> Also, does this make sense to CC to stable?
>>
>> Probably not, as the HW never worked, so it is not a regression.
>>
>> Thanks,
>>
>> M.
>>
>
>
next prev parent reply other threads:[~2018-07-12 2:31 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-11 2:27 [PATCH 0/2] Allwinner A64 timer workaround Samuel Holland
2018-05-11 2:27 ` [PATCH 1/2] arm64: arch_timer: Workaround for Allwinner A64 timer instability Samuel Holland
2018-05-11 8:26 ` Maxime Ripard
2018-05-11 8:48 ` Marc Zyngier
2018-05-11 15:08 ` Samuel Holland
2018-05-26 15:15 ` André Przywara
2018-05-11 2:27 ` [PATCH 2/2] arm64: dts: allwinner: a64: Enable A64 timer workaround Samuel Holland
2018-05-11 9:24 ` [PATCH 0/2] Allwinner " Andre Przywara
2018-07-03 15:09 ` Marc Zyngier
2018-07-03 18:42 ` Samuel Holland
2018-07-04 8:16 ` Marc Zyngier
2018-07-04 8:19 ` Chen-Yu Tsai
2018-07-04 8:23 ` Daniel Lezcano
2018-07-04 8:39 ` Marc Zyngier
2018-07-04 10:00 ` Thomas Gleixner
2018-07-04 13:08 ` [linux-sunxi] " Andre Przywara
2018-07-04 14:31 ` Thomas Gleixner
2018-07-04 14:44 ` Andre Przywara
2018-07-04 15:01 ` Marc Zyngier
2018-07-04 15:15 ` Andre Przywara
2018-07-04 15:30 ` Marc Zyngier
2018-07-04 15:23 ` Samuel Holland
2018-07-04 15:14 ` Thomas Gleixner
2018-07-04 15:43 ` Andre Przywara
2018-07-04 19:49 ` Thomas Gleixner
2018-07-04 8:41 ` Daniel Lezcano
2018-07-12 2:23 ` Samuel Holland [this message]
2018-07-04 9:06 ` Maxime Ripard
2018-07-04 8:41 ` Daniel Lezcano
2018-07-04 12:52 ` [linux-sunxi] " Andre Przywara
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