On Sat, 30 Jan 2021 13:12:32 +0100 Mark Kettenis kettenis@openbsd.org wrote:
On implementations that support VHE, the layout of the CPTR_EL2 register depends on whether HCR_EL2.E2H is set. Check this bit and and set the aprropriate bits 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 machine with Apple's M1 SoC.
That looks correct, I compared the bits against the manual. TCR_EL2 and CNTHCTL_EL2 are also different, have you checked that U-Boot's usage of it is compatible with E2H=1?
And we should probably allow SVE for non-VHE systems as well, but this is probably another patch.
One nit below.
Signed-off-by: Mark Kettenis kettenis@openbsd.org
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..a259717e67 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_host /* HCR_EL2.E2H */
el2_host sounds a bit ambiguous, can we use el2_vhe instead? That would also point to the term "VHE", which is more known (and searchable) than the "E2H" bit.
Cheers, Andre
mov x0, #0x33ff msr cptr_el2, x0 /* Enable FP/SIMD */ b 0f +el2_host:
- 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 */