Errata on multiplatform kernels

[Jon Masters]

On 12/11/2012 07:51 PM, Russell King - ARM Linux wrote:
> On Tue, Dec 11, 2012 at 07:41:18PM -0500, Jon Masters wrote:
>> On 12/11/2012 01:01 PM, Tony Lindgren wrote:
>>> * Olof Johansson <olof at lixom.net> [121210 21:38]:
>>>> Hi,
>>>>
>>>> On Mon, Dec 10, 2012 at 9:20 PM, Tony Prisk <linux at prisktech.co.nz> wrote:
>>>>> How are errata handled on multiplatform kernels?
>>>>>
>>>>> There don't appear to be any errata selected by default in any of the
>>>>> current multiplatform options, but presumably it will happen eventually.
>>>>>
>>>>> Does that mean the errata will be applied to all machines that boot with
>>>>> the errata selected, even if not required?
>>>>
>>>> Yes. To date I believe most errata we have are just performance hits
>>>> on platforms that don't need it.
>>>>
>>>> Other architectures have in some cases added runtime patching (out) of
>>>> workarounds that aren't needed on the current platform for the ones
>>>> that have significant performance impact. I'm guessing we'll end up
>>>> with something similar eventually but until then we'll try to just go
>>>> with the superset of needed errata.
>>>
>>> We can't enable any of the errata if there's a chance that it will behave
>>> in a different way for secure mode devices compared to non-secure devices.
>>>
>>> The discussion is in the thread "[PATCH] ARM: Fix errata 751472 handling
>>> on Cortex-A9 r1p*".
>>>
>>> The conclusion was that we cannot enable any errata for multiplatform,
>>> and must assume the errata is handled by the bootloader. Multiplatform
>>> image is already broken for at least omap4 as 751472 is selected.
>>
>> On some platforms with a PL310 we have errata 588369 and 727915
>> (especially enabled on OMAP4 targets) which will cause an external abort
>> when enabled and then booted on highbank systems. This has taken the
>> last couple of days on and off to track down. So I guess we need to
>> basically disable these in our (Fedora) multiplatform kernel and then
>> assume that e.g. PandaBoard will implement some U-Boot fix if it needs
>> to have one? Not sure exactly what that fix is going to look like :)
> 
> Neither 588369 nor 727915 are something a boot loader can do - they have
> to be done in the kernel.  If they're causing highbank systems to fail
> that needs to be debugged.

Exactly. I can see no way this can be done in the bootloader code either.

> My guess is that highbank is another non-secure system, and the L2x0
> code is trying to use pl310_set_debug() which will fail on non-secure
> systems as the 'set_debug' hook is not being overriden.

Right, and right again.

> If there was a way to tell that we're running on a non-secure system,
> we could automatically point set_debug() to a nop function, but it
> would be far more preferable for highbank to provide the hook.  (That
> could be itself a no-op if it doesn't require the work-around.)

I leave that one to Rob :)

Jon.