Re: [PATCH 0/2] Allwinner A64 timer workaround

From: Samuel Holland
Date: Tue Jul 03 2018 - 14:42:46 EST

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) â 150 should be a conservative iteration limit?

Also, does this make sense to CC to stable?