Re: [PATCH v5 12/30] arm64/sve: Low-level CPU setup

["Alex Bennée" <alex.bennee@linaro.org>]

Dave Martin <Dave.Martin@arm.com> writes:

> To enable the kernel to use SVE, SVE traps from EL1 to EL2 must be
> disabled.  To take maximum advantage of the hardware, the full
> available vector length also needs to be enabled for EL1 by
> programming ZCR_EL2.LEN.  (The kernel will program ZCR_EL1.LEN as
> required, but this cannot override the limit set by ZCR_EL2.)
>
> This patch makes the appropriate changes to the EL2 early setup
> code.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Alex Bennée <alex.bennee@linaro.org>
>
> ---
>
> **Dropped at v3** Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
> (Due to significant changes to the logic.)

Have it back:

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

> ---
>  arch/arm64/kernel/head.S | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index cfa90a4..67e86a0 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -524,8 +524,19 @@ CPU_LE(	movk	x0, #0x30d0, lsl #16	)	// Clear EE and E0E on LE systems
>  	mov	x0, #0x33ff
>  	msr	cptr_el2, x0			// Disable copro. traps to EL2
>
> +	/* SVE register access */
> +	mrs	x1, id_aa64pfr0_el1
> +	ubfx	x1, x1, #ID_AA64PFR0_SVE_SHIFT, #4
> +	cbz	x1, 7f
> +
> +	bic	x0, x0, #CPTR_EL2_TZ		// Also disable SVE traps
> +	msr	cptr_el2, x0			// Disable copro. traps to EL2
> +	isb
> +	mov	x1, #ZCR_ELx_LEN_MASK		// SVE: Enable full vector
> +	msr_s	SYS_ZCR_EL2, x1			// length for EL1.
> +
>  	/* Hypervisor stub */
> -	adr_l	x0, __hyp_stub_vectors
> +7:	adr_l	x0, __hyp_stub_vectors
>  	msr	vbar_el2, x0
>
>  	/* spsr */