xorg broken on Beaglebone black revision 300438

[Ian Lepore]

On Tue, 2016-05-24 at 14:35 -0700, Mark Millard wrote:
> Quoting from Otacílio Tue May 24 00:06:10 UTC 2016 and its locore
> -v6.S changes:
> 
> > -    orr    r7, #CPU_CONTROL_UNAL_ENABLE
> > -    orr    r7, #CPU_CONTROL_AFLT_ENABLE
> > +    bic    r7, #CPU_CONTROL_UNAL_ENABLE
> > +    bic    r7, #CPU_CONTROL_AFLT_ENABLE
> 
> -r295256 (2016-Feb-14) changed from:
> 
> bic     r7, #CPU_CONTROL_UNAL_ENABLE
> 
> to:
> 
> orr     r7, #CPU_CONTROL_UNAL_ENABLE
> 
> in two places (moving it a few lines down for each example as well).
> So this much of the proposed changes would be reverting the -r295256
> change. The check in comment indicates the bit is RAO/SBOP for armv7.
> For armv6 the check in comment claims it controls armv5 compatible
> alignment support.
> 
> But:
> 
> orr     r7, #CPU_CONTROL_AFLT_ENABLE
> 
> has been in locore-v6.S since the file's first checkin. So this
> change to bic here be new.
> 
> What is the FreeBSD intent for each of the two new settings for
> armv7? armv6?
> 

It was always wrong to clear CPU_CONTROL_UNAL_ENABLE on armv7 (it's
documented as RAO/SBOP).  Setting it on armv6 makes the v6 (which is
only the RPi in our world) behave the same as v7.  So that change was
just a bugfix.

I think FreeBSD is the only major OS left that is enforcing strict
alignment on armv6/v7 and it causes a lot of trouble for ports and
other 3rd party software, and prevents us from enabling certain
compiler options and optimizations.  I'm very close to a commit to stop
enforcing strict alignment (clear rather than CPU_CONTROL_AFLT_ENABLE).
 I've been testing it yesterday and today, and haven't run into any
trouble at all.

-- Ian