[PATCH v3] ARM: vfp: fix save and restore when running on pre-VFPv3 and CONFIG_VFPv3 set

[Tony Lindgren]

* Paul Walmsley <paul at pwsan.com> [121014 22:26]:
> 
> After commit 846a136881b8f73c1f74250bf6acfaa309cab1f2 ("ARM: vfp: fix
> saving d16-d31 vfp registers on v6+ kernels"), the OMAP 2430SDP board
> started crashing during boot with omap2plus_defconfig:
> 
> [    3.875122] mmcblk0: mmc0:e624 SD04G 3.69 GiB
> [    3.915954]  mmcblk0: p1
> [    4.086639] Internal error: Oops - undefined instruction: 0 [#1] SMP ARM
> [    4.093719] Modules linked in:
> [    4.096954] CPU: 0    Not tainted  (3.6.0-02232-g759e00b #570)
> [    4.103149] PC is at vfp_reload_hw+0x1c/0x44
> [    4.107666] LR is at __und_usr_fault_32+0x0/0x8
> 
> It turns out that the context save/restore fix unmasked a latent bug
> in commit 5aaf254409f8d58229107b59507a8235b715a960 ("ARM: 6203/1: Make
> VFPv3 usable on ARMv6").  When CONFIG_VFPv3 is set, but the kernel is
> booted on a pre-VFPv3 core, the code attempts to save and restore the
> d16-d31 VFP registers.  These are only present on non-D16 VFPv3+, so
> this results in an undefined instruction exception.  The code didn't
> crash before commit 846a136 because the save and restore code was
> only touching d0-d15, present on all VFP.
> 
> Fix by implementing a request from Russell King to add a new HWCAP
> flag that affirmatively indicates the presence of the d16-d31
> registers:
> 
>    http://marc.info/?l=linux-arm-kernel&m=135013547905283&w=2
> 
> and some feedback from Måns to clarify the name of the HWCAP flag.
> 
> Signed-off-by: Paul Walmsley <paul at pwsan.com>
> Cc: Tony Lindgren <tony at atomide.com>
> Cc: Russell King <rmk+kernel at arm.linux.org.uk>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Dave Martin <dave.martin at linaro.org>
> Cc: Måns Rullgård <mans.rullgard at linaro.org>

This fixes the error above on my 2430sdp:

Tested-by: Tony Lindgren <tony at atomide.com>