Re: [PATCH] arm: Fix mounting root on omaps with CPU_V6 and CPU_V7

[Tony Lindgren <tony@atomide.com>]

* Catalin Marinas <catalin.marinas@arm.com> [100317 11:04]:
> On Wed, 2010-03-17 at 17:57 +0000, Tony Lindgren wrote:
> > Here's an updated version of this patch with more details.
> > 
> > Looks like VFPv3 is only available on V7:
> > 
> > http://www.arm.com/products/processors/technologies/vector-floating-point.php
> 
> But does it cause any problem if the feature is enabled in the kernel?
> The vfp_init() code should check for its presence and set the hwcap
> accordingly.

Yeah, it causes the problem posted in the patch description. I took a
quick look at it and at least the VFPFMRX in vfpmacros.h for CONFIG_VFPv3
is a problem.

Also I think we would need to have separate vfp_get_double functions
in vfphw.S for VFPv2 and 3 that get used based on the features.
 
> Ideally, we should fix the VFP handling code to cope with dynamic
> detection.

I agree, being able to boot the same kernel and avoiding tens of
recompiles to test something is a major time saver :)
 
> > HAS_TLS reg is only on ARM11 starting with r1p0:
> > 
> > http://infocenter.arm.com/help/topic/com.arm.doc.ddi0211k/Babeihid.html
> > 
> > So that explains why it won't work on omap2420 as it's r0p2.
> 
> Same here, would it work with dynamic detection?

Hmm I believe here the problem is __switch_to in entry-armv.S.
I don't think we want to dynamically test it every time.. Or
at least it would have to be optimized out in most cases.

> I would like to get v6+v7 support working fine together on RealView
> boards as well (though not much spare time) but without disabling the
> features that are present on v7 if they can be detected at run-time.

I totally agree with you there.

Regards,

Tony