[U-Boot] [PATCH 1/2] arm: timer: factor out FSL arch timer erratum workaround

[André Przywara]

On 07/03/2018 09:59 PM, Alexander Graf wrote:
> 
> 
>> Am 03.07.2018 um 22:51 schrieb Andreas Färber <afaerber at suse.de>:
>>
>>> Am 03.07.2018 um 01:08 schrieb Andreas Färber:
>>>> Am 02.07.2018 um 10:01 schrieb Jagan Teki:
>>>>> On Wed, Jun 27, 2018 at 6:12 AM, Andre Przywara <andre.przywara at arm.com> wrote:
>>>>> At the moment we have the workaround for the Freescale arch timer
>>>>> erratum A-008585 merged into the generic timer_read_counter() routine.
>>>>> Split those two up, so that we can add other errata workaround more
>>>>> easily. Also add an explaining comment on the way.
>>>>>
>>>>> Signed-off-by: Andre Przywara <andre.przywara at arm.com>
>>>>> ---
>>>>
>>>> Applied both patches, to u-boot-sunxi/master
>>>
>>> Tested both on top of v2018.07-rc2, fixes the boot for me.
>>
>> Actually I saw it again just now, without having touched U-Boot at all.
>> Unplugged power, retried, worked. So it seems we've reduced the
>> likelihood, but something might still be astray...
> 
> So maybe we need to instead apply some logic that loops until cnt == prev_cnt+1?
> 
> Also, is there any way to just trap counter reads from EL3?

I can't find anything for EL3, and I believe we can't trap the virtual
timer at all except for EL0. Besides, that would be rather costly. The
current solution normally gets away with just one sysreg read, so it
would be just the comparison overhead we have to pay. You don't want to
give this away easily.

> It'd be quite tedious to fix up all OSs out there.

Well, bad luck, it's a hardware erratum - and not the first one in this
area. So chances are you can add just another one quite easily, as we do
in Linux - where we actually have somewhat of an "arch timer errata
framework".

Cheers,
Andre.