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

[Suzuki K Poulose]

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 at 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/


Suzuki