Re: [PATCH] ARM: Fix errata 751472 handling on Cortex-A9 r1p*

[Tony Lindgren <tony@atomide.com>]

* Rob Herring <robherring2@gmail.com> [121114 16:56]:
> On 11/14/2012 04:21 PM, Tony Lindgren wrote:
> > * Rob Herring <robherring2@gmail.com> [121114 13:59]:
> >> On 11/14/2012 02:32 PM, Tony Lindgren wrote:
> >>>
> >>> Checking for the bit already set should work in this case, I'll post
> >>> a patch for that shortly.
> >>
> >> Can you actually read the state of the diagnostic register in non-secure
> >> mode? If you can on the A9, is the same true on A8 or others?
> > 
> > Looks like it can be read on at least TI omap 4430 which is A9.
> > But it reads as zero, so the below patch is what I came up with.
> > 
> > No idea if assuming that zero value for the diagnostic register
> > is safe.. What's the default value of the diagnostic register supposed
> > to be?
> 
> RTFM. Oh, wait it's a super secret, undocumented register. We shouldn't
> even be talking about it.

WITFM? :)
 
> It could vary by rev, but I see 0 for the reset value, so this would not
> work if the bootloader did not do any setup of the diagnostic register.

OK
 
> One way to determine secure mode on the A9 would be seeing if you can
> change the auxcr register. Something like this (untested):
> 
> mrc	p15, 0, r0, c1, c0, 1; Read ACTLR
> eor	r1, r0, #0x100		; Modify alloc in 1 way
> mcr	p15, 0, r1, c1, c0, 1
> mrc	p15, 0, r2, c1, c0, 1; Read ACTLR
> mcr	p15, 0, r0, c1, c0, 1	; Restore original value
> cmp	r1, r2
> bne	skip_errata
> 
> 
> It would be good to do this test for all the errata rather than just
> this one.

I recall writes to the aux control registers producing an exception
on secure A8 based omaps, but I'll give that a try when I have a
chance.

Regards,

Tony