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

[Li Li]

Nicolas,

Thanks for the explanation. :)

I noticed what you mentioned. Actually, Kconfig says TLS EMU might be
used in some "old" (e.g. pre-armv6) SMP platforms without TLS
register. In such a case, could we still ensure it's SMP safe by a
single ldr?

Thanks,
Lea

On Fri, Apr 8, 2011 at 9:19 PM, Nicolas Pitre <nico at fluxnic.net> wrote:
> On Fri, 8 Apr 2011, Li Li wrote:
>
>> Dears,
>>
>> I cannot understand how TLS EMU ensure it's SMP safe, because get_tls
>> helper (at 0xffff0fe0) just read the value from 0xffff0ff0. But all
>> SMP cores should have the exact same mapping to the vectors page (at
>> 0xffff0000). So various threads running on different SMP cores at the
>> same time would get the same emulated TLS value (instead of thread
>> specific value set via set_tls). Could anybody explain this a little
>> bit?
>
> On SMP the hardware TLS register is always available, therefore the TLS
> value is not stored at 0xffff0ff0.  The code actually installed at
> 0xffff0fe0 is modified at boot time by kuser_get_tls_init to select
> either the ldr or the mrc instruction to retrieve the TLS value.
>
>
> Nicolas
>