[PATCH 1/4] arm64/sysreg: Allow a 'Mapping' descriptor for system registers

[Mark Rutland]

On Sat, Dec 07, 2024 at 07:07:37PM +0000, Marc Zyngier wrote:
> *EL02 and *_EL12 system registers are actually only accessors for
> EL0 and EL1 registers accessed from EL2 when HCR_EL2.E2H==1. They
> do not have fields of their own.
> 
> To that effect, introduce a 'Mapping' entry, describing which
> system register an _EL12 register maps to.
> 
> Implementation wise, this is handled the same was as Fields,
> which ls only a comment.
> 
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/tools/gen-sysreg.awk | 2 +-
>  arch/arm64/tools/sysreg         | 7 +++++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/tools/gen-sysreg.awk b/arch/arm64/tools/gen-sysreg.awk
> index d1254a056114e..1a2afc9fdd42e 100755
> --- a/arch/arm64/tools/gen-sysreg.awk
> +++ b/arch/arm64/tools/gen-sysreg.awk
> @@ -206,7 +206,7 @@ END {
>  
>  # Currently this is effectivey a comment, in future we may want to emit
>  # defines for the fields.
> -/^Fields/ && block_current() == "Sysreg" {
> +(/^Fields/ || /^Mapping/) && block_current() == "Sysreg" {
>  	expect_fields(2)
>  
>  	if (next_bit != 63)
> diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
> index b081b54d6d227..b6846c601df6c 100644
> --- a/arch/arm64/tools/sysreg
> +++ b/arch/arm64/tools/sysreg
> @@ -38,6 +38,13 @@
>  # Fields	<fieldsname>
>  # EndSysreg
>  
> +# For register names indicating a cross-EL access (*_EL12, *EL02),
> +# a Mapping entry describes the register it actually accesses:

It might be better to say:

| For VHE aliases (*_EL12, *_EL02) of system registers, a Mapping entry
| describes the register the alias actually accesses:

... and with that'd it's probably best to place this above the
description of SysregFields, so that people see this first and don't
copy the anti-pattern you're trying to remove.

For SysregFields we could clarify the existing wording to:

| Where multiple system regsiters are not VHE aliases but share a common
| layout, a SysregFields block can be used to describe the shared
| layout:

With or without those changes:

Acked-by: Mark Rutland <mark.rutland at arm.com>

Mark.

> +
> +# Sysreg 	<name_EL12>	<op0> 	<op1>	<crn>	<crm>	<op2>
> +# Mapping	<name_EL1>
> +# EndSysreg
> +
>  # For ID registers we adopt a few conventions for translating the
>  # language in the ARM into defines:
>  #
> -- 
> 2.39.2
>