Subject: [PATCH 1/2] arm: Replace CONFIG_HAS_TLS_REG with HWCAP_TLS and check for it on V6

From: [email-masked] (Tony Lindgren)
Date: Wed, 23 Jun 2010 12:28:44 +0300

* Russell King - ARM Linux <[email-masked]> [100623 11:06]:
> On Wed, Jun 23, 2010 at 10:39:13AM +0300, Tony Lindgren wrote:
> > Yeah that can be done for __kuser_get_tls if it's always writable.
> > But __switch_to is trickier because of the CONFIG_MMU ifdefs there.
> 
> And impossible with XIP kernels.
> 
> > What if we have optional __switch_to and __kuser_get_tls implementations
> > in the mm/proc-*.S files that get copied over the current locations
> > if implemented?
> 
> Also problematical with XIP - if we go down the route of implementing
> these by copying code fragments into the kernel, we need to strip out
> XIP support or implement a second way.  Obviously having a second way
> adds maintainence burden, and the second way will probably lose out
> on updates.

How about if we implement the default XIP-safe unoptimized functions,
with minimal iffdeffery and then allow optional override for non-XIP
kernels from mm/proc-*.S files?

Regards,

Tony