ARM: add support for kernel mode NEON
In order to safely support the use of NEON instructions in
kernel mode, some precautions need to be taken:
- the userland context that may be present in the registers (even
if the NEON/VFP is currently disabled) must be stored under the
correct task (which may not be 'current' in the UP case),
- to avoid having to keep track of additional vfpstates for the
kernel side, disallow the use of NEON in interrupt context
and run with preemption disabled,
- after use, re-enable preemption and re-enable the lazy restore
machinery by disabling the NEON/VFP unit.
This patch adds the functions kernel_neon_begin() and
kernel_neon_end() which take care of the above. It also adds
the Kconfig symbol KERNEL_MODE_NEON to enable it.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 136f263..d6068b4 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -2197,6 +2197,13 @@
Say Y to include support code for NEON, the ARMv7 Advanced SIMD
Extension.
+config KERNEL_MODE_NEON
+ bool "Support for NEON in kernel mode"
+ default n
+ depends on NEON
+ help
+ Say Y to include support for NEON in kernel mode.
+
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