[PATCH] arm64/sve: Document firmware support requirements in Kconfig

[Dave.Martin@arm.com (Dave Martin)]

On Fri, Mar 23, 2018 at 05:27:32PM +0000, Suzuki K Poulose wrote:
> On 21/03/18 11:54, Dave Martin wrote:
> >Use of SVE by EL2 and below requires explicit support in the
> >firmware.  There is no means to hide the presence of SVE from EL2,
> >so a kernel configured with CONFIG_ARM64_SVE=y will typically not
> >work correctly on SVE capable hardware unless the firmware does
> >include the appropriate support.
> >
> >This is not expected to pose a problem in the wild, since platform
> >integrators are responsible for ensuring that they ship up-to-date
> >firmware to support their hardware.  However, developers may hit
> >the issue when using mismatched compoments.
> >
> >In order to draw attention to the issue and how to solve it, this
> >patch adds some Kconfig text giving a brief explanation and details
> >of compatible firmware versions.
> >
> >Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> >---
> >
> >No functional change, but it would be good to get this explanatory text
> >merged since developers who try Linux on SVE-enabled models may hit
> >this problem, and fixed versions of ARM TF and the bootwrapper are now
> >available.
> >
> >  arch/arm64/Kconfig | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> >
> >diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> >index 7381eeb..e6fa47b 100644
> >--- a/arch/arm64/Kconfig
> >+++ b/arch/arm64/Kconfig
> >@@ -1104,6 +1104,23 @@ config ARM64_SVE
> >  	  To enable use of this extension on CPUs that implement it, say Y.
> >+	  Note that for architectural reasons, firmware _must_ implement SVE
> >+	  support when running on SVE capable hardware.  The required support
> >+	  is present in:
> >+
> >+	    * version 1.5 and later of the ARM Trusted Firmware
> >+	    * the AArch64 boot wrapper since commit 5e1261e08abf
> >+	      ("bootwrapper: SVE: Enable SVE for EL2 and below").
> >+
> >+	  For other firmware implementations, consult the firware documentation
> 
> minor nit: 	s/firware/firmware/

Thanks, I'll repost with that fixed.

Cheers
---Dave