[PATCH v3] armv8: Handle EL2 Host mode

[Mark Kettenis]

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>
---

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