Re: [PATCH v2 5/6] aarch64: Support PSCI for Armv8-R AArch64

[Mark Rutland <mark.rutland@arm.com>]

On Tue, Jul 16, 2024 at 03:29:05PM +0100, Luca Fancellu wrote:
> Add support for PSCI when booting Linux on Armv8-R AArch64,
> allow the autoconf parameter --enable-psci to take an argument
> which is the conduit to be used, it can be empty or 'smc' to
> select the smc conduit, it can be 'hvc' for the hvc conduit.
> 
> Depending on the selected conduit, the vector table will be
> installed on the VBAR_EL3 or VBAR_EL2 register.
> 
> Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>
> Reviewed-by: Andre Przywara <andre.przywara@arm.com>
> ---
> v2 changes:
>  - Add Andre R-by
> ---
>  Makefile.am         |  5 ++++-
>  arch/aarch64/init.c | 15 ++++++++++++---
>  configure.ac        | 16 +++++++++++-----
>  3 files changed, 27 insertions(+), 9 deletions(-)
> 
> diff --git a/Makefile.am b/Makefile.am
> index 6ebece25b230..34fbfb1f4ff8 100644
> --- a/Makefile.am
> +++ b/Makefile.am
> @@ -49,11 +49,14 @@ endif
>  
>  if PSCI
>  DEFINES		+= -DPSCI
> +if PSCI_HVC
> +DEFINES		+= -DPSCI_HVC
> +endif
>  ARCH_OBJ	+= psci.o
>  COMMON_OBJ	+= psci.o
>  PSCI_NODE	:= psci {				\
>  			compatible = \"arm,psci\";	\
> -			method = \"smc\";		\
> +			method = \"$(PSCI_METHOD)\";	\
>  			cpu_on = <$(PSCI_CPU_ON)>;	\
>  			cpu_off = <$(PSCI_CPU_OFF)>;	\
>  		   };
> diff --git a/arch/aarch64/init.c b/arch/aarch64/init.c
> index 9402a01b9dca..9b8bd8723dba 100644
> --- a/arch/aarch64/init.c
> +++ b/arch/aarch64/init.c
> @@ -179,10 +179,19 @@ extern char psci_vectors[];
>  
>  bool cpu_init_psci_arch(void)
>  {
> -	if (mrs(CurrentEL) != CURRENTEL_EL3)
> +	switch (mrs(CurrentEL)) {
> +#if !defined(PSCI_HVC)
> +	case CURRENTEL_EL3:
> +		msr(VBAR_EL3, (unsigned long)psci_vectors);
> +		break;
> +#else
> +	case CURRENTEL_EL2:
> +		msr(VBAR_EL2, (unsigned long)psci_vectors);
> +		break;
> +#endif
> +	default:
>  		return false;
> -
> -	msr(VBAR_EL3, (unsigned long)psci_vectors);
> +	}
>  	isb();
>  
>  	return true;
> diff --git a/configure.ac b/configure.ac
> index 9e3b7226cd69..44459a4c849e 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -83,13 +83,19 @@ AS_IF([test "x$X_IMAGE" != "x"],
>  # Allow a user to pass --enable-psci
>  AC_ARG_ENABLE([psci],
>  	AS_HELP_STRING([--disable-psci], [disable the psci boot method]),
> -	[USE_PSCI=$enableval], [USE_PSCI="yes"])
> -AM_CONDITIONAL([PSCI], [test "x$USE_PSCI" = "xyes"])
> -AS_IF([test "x$USE_PSCI" = "xyes"], [], [USE_PSCI=no])
> -
> -AS_IF([test "x$USE_PSCI" != "xyes" -a "x$KERNEL_ES" = "x32"],
> +	[case "${enableval}" in
> +		yes|smc) USE_PSCI=smc ;;
> +		hvc) USE_PSCI=hvc ;;
> +		no) ;;
> +		*) AC_MSG_ERROR([Bad value "${enableval}" for --enable-psci. Use "smc" or "hvc"]) ;;
> +	esac])
> +AM_CONDITIONAL([PSCI], [test "x$USE_PSCI" = "xyes" -o "x$USE_PSCI" = "xsmc" -o "x$USE_PSCI" = "xhvc"])
> +AM_CONDITIONAL([PSCI_HVC], [test "x$USE_PSCI" = "xhvc"])
> +
> +AS_IF([test "x$USE_PSCI" = "xno" -a "x$KERNEL_ES" = "x32"],
>  	[AC_MSG_ERROR([With an AArch32 kernel, boot method must be PSCI.])]
>  )
> +AC_SUBST([PSCI_METHOD], [$USE_PSCI])

As of this patch, if I build with --enable-psci=hvc, and boot on
ARMv8-A, it'll fail at boot time, since the boot-wrapper won't fix up
the SPSR (and will enter the kernel at EL2), and HVC will go to that
kernel.

I think that we either need to add support for dropping to EL1 in
ARMv8-A, or we should have an option to build for ARMv8-R specifically,
where we can automatically fix up the PSCI conduit.

Mark.