[PATCH v3] armv8: Handle EL2 Host mode

[Mark Kettenis]

> From: Mark Kettenis <kettenis at openbsd.org>
> Date: Wed, 10 Feb 2021 19:25:53 +0100
> 
> On implementations that support VHE, the layout of the CPTR_EL2
> register depends on whether HCR_EL2.E2H is set.  If the bit is
> set, CPTR_EL2 uses the same layout as CPACR_EL1 and can in fact
> be accessed through that register.  In that case, jump to the
> EL1 code to enable access to the FP/SIMD registers.  This allows
> U-Boot to run on systems that pass control to U-Boot in EL2 with
> EL2 Host mode enabled such as machines using Apple's M1 SoC.
> 
> Signed-off-by: Mark Kettenis <kettenis at openbsd.org>
> ---

Please disregard, I forgot to commit the actual change.


> v3: use EL1 codepath when HCR_EL2.E2H is set
>     suggested by Marc Zyngier <maz at kernel.org>
> 
> v2: rename label
> 
>  arch/arm/cpu/armv8/start.S | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/arm/cpu/armv8/start.S b/arch/arm/cpu/armv8/start.S
> index 662449156b..979dcfef35 100644
> --- a/arch/arm/cpu/armv8/start.S
> +++ b/arch/arm/cpu/armv8/start.S
> @@ -133,9 +133,15 @@ pie_fixup_done:
>  #endif
>  	b	0f
>  2:	set_vbar	vbar_el2, x0
> +	mrs	x0, hcr_el2
> +	tbnz	x0, #34, el2_vhe		/* HCR_EL2.E2H */
>  	mov	x0, #0x33ff
>  	msr	cptr_el2, x0			/* Enable FP/SIMD */
>  	b	0f
> +el2_vhe:
> +	mov	x0, #3 << 20
> +	msr	cptr_el2, x0			/* Enable FP/SIMD */
> +	b	0f
>  1:	set_vbar	vbar_el1, x0
>  	mov	x0, #3 << 20
>  	msr	cpacr_el1, x0			/* Enable FP/SIMD */
> -- 
> 2.30.0
> 
>