ARM errata 430973 on multi platform kernels

[Grazvydas Ignotas]

On Tue, Apr 7, 2015 at 5:23 AM, Tony Lindgren <tony at atomide.com> wrote:
> * Matthijs van Duin <matthijsvanduin at gmail.com> [150406 11:15]:
>>
>> On 6 April 2015 at 19:42, Tony Lindgren <tony at atomide.com> wrote:
>> > Hmm but it still seems to do something also on cortex-a8 r3p2 that
>> > is supposedly not affected by 430973.. Based on my tests so far, at least
>> > armhf running cpuburn-a8 in the background and doing apt-get update
>> > segfaults constantly without flush BTAC/BTB. This seems to be the case
>> > no matter how the aux ctrl reg bits are set..
>>
>> That sounds.... really odd.  The TRM is fairly explicit about BTB
>> flush executing as nop when IBE is not set. Of course the TRM is not
>> exactly flawless, but still...
>
> Oops, sorry user error.. I was trying to clear IBE as a banked register
> like L2 enable bit and of course it did not get cleared.. Clearing it
> with a smc call really clears it. And in that case my test case seems to
> work reliably on r3p2 without erratum 430973 enabled.

May I ask how do you perform the smc call? I wanted to clear IBE too
to experiment, but it just hangs my board, even if I just write back
the same value. Here is what I do:

        asm ("mrc p15, 0, %0, c1, c0, 1" : "=r"(val));

        asm (".arch_extension sec\n\t"
             "mov r0,  %0\n"
             "mov r12, #3\n"
             "smc #0\n"
             :: "r"(val) : "r0", "r12");

I just run this from a sysfs write handler, does it need to be run on
SRAM or something?

Gražvydas