[boot-wrapper][PATCH] aarch64: Enable SPE for the non-secure world

[André Przywara]

On 31/07/2020 10:44, Alexandru Elisei wrote:

Hi,

> MDCR_EL3.NSPB resets to an UNKNOWN value. Configure it to allow the
> profiling buffer to use non-secure memory and to permit direct register
> accesses from the non-secure world.
> 
> So far, we haven't programmed MDCR_EL3 explicitly even though there are
> other fields which reset to an UNKNOWN value. The majority of those, when
> cleared, allow lower exception levels to use the features they control; for
> the other fields we don't have support yet.  Reset the register to zero
> with the exception of MDCR_EL3.NSPB.
> 
> Signed-off-by: Alexandru Elisei <alexandru.elisei at arm.com>
> ---
> Tested on the model, with ARMv8.2 enabled and disabled (no SPE present).
> 
>  arch/aarch64/boot.S | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/arch/aarch64/boot.S b/arch/aarch64/boot.S
> index 74705cded338..f821b0175d4b 100644
> --- a/arch/aarch64/boot.S
> +++ b/arch/aarch64/boot.S
> @@ -55,6 +55,17 @@ _start:
>  
>  	msr	cptr_el3, xzr			// Disable copro. traps to EL3
>  
> +	mov	x0, xzr
> +	mrs	x1, id_aa64dfr0_el1
> +	ubfx	x1, x1, #32, #4
> +	cbz	x1, 1f
> +
> +	// Enable SPE for the non-secure world.
> +	ldr	x1, =(0x3 << 12)
> +	orr	x0, x0, x1

Just a nit, but 0x3000 is one of the (few) immediate patterns that can
be encoded directly in ORR. So you can save the ldr.

Other than that:

Reviewed-by: Andre Przywara <andre.przywara at arm.com>

Cheers,
Andre


> +
> +1:	msr	mdcr_el3, x0			// Disable traps to EL3
> +
>  	mrs	x0, id_aa64pfr0_el1
>  	ubfx	x0, x0, #32, #4			// SVE present?
>  	cbz	x0, 1f				// Skip SVE init if not
>