Re: [PATCH 11/12] ras: add DeviceTree estatus provider driver

[Will Deacon <will@kernel.org>]

On Thu, Dec 18, 2025 at 01:42:47PM +0000, Ahmed Tiba wrote:
> On Thu, 18 Dec 2025 12:13:25PM +0000, Will Deacon wrote:
> >> Introduce a platform driver that maps the CPER status block described
> >> in DeviceTree, feeds it into the estatus core and handles either IRQ- or
> >> poll-driven notifications. Arm64 gains a FIX_ESTATUS_IRQ slot so the
> >> driver can safely map the shared buffer while copying records.
> >>
> >> Signed-off-by: Ahmed Tiba <ahmed.tiba@arm.com>
> >> ---
> >>  MAINTAINERS                     |   1 +
> >>  arch/arm64/include/asm/fixmap.h |   5 +
> >>  drivers/ras/Kconfig             |  14 ++
> >>  drivers/ras/Makefile            |   1 +
> >>  drivers/ras/estatus-dt.c        | 318 ++++++++++++++++++++++++++++++++
> >>  include/linux/estatus.h         |   3 +-
> >>  6 files changed, 341 insertions(+), 1 deletion(-)
> >>  create mode 100644 drivers/ras/estatus-dt.c
> >>
> >> diff --git a/MAINTAINERS b/MAINTAINERS
> >> index 6b2ef2ddc0c7..5567d5e82053 100644
> >> --- a/MAINTAINERS
> >> +++ b/MAINTAINERS
> >> @@ -21761,6 +21761,7 @@ RAS ERROR STATUS
> >>  M:   Ahmed Tiba <ahmed.tiba@arm.com>
> >>  S:   Maintained
> >>  F:   Documentation/devicetree/bindings/ras/arm,ras-ffh.yaml
> >> +F:   drivers/ras/estatus-dt.c
> >>  F:   drivers/firmware/efi/estatus.c
> >>  F:   include/linux/estatus.h
> >> 
> >> diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
> >> index 65555284446e..85ffba87bab9 100644
> >> --- a/arch/arm64/include/asm/fixmap.h
> >> +++ b/arch/arm64/include/asm/fixmap.h
> >> @@ -64,6 +64,11 @@ enum fixed_addresses {
> >>  #endif
> >>  #endif /* CONFIG_ACPI_APEI_GHES */
> >> 
> >> +#ifdef CONFIG_RAS_ESTATUS_DT
> >> +     /* Used for ESTATUS mapping from assorted contexts */
> >> +     FIX_ESTATUS_IRQ,
> >> +#endif /* CONFIG_RAS_ESTATUS_DT */
> >
> > Why do we need this in addition to the four existing GHES slots? The DT
> > code doesn't use it and I was assuming that the ACPI code would continue
> > to use the existing irq; is that not the case?
> 
> 
> We still need a dedicated slot when only the DT provider is built.
> All four GHES slots are defined as part of the ACPI implementation,
> so they are not present in a DT-only configuration.
> 
> The estatus core always requests a fixmap index from each provider
> before copying a CPER record. As a result, the DT driver must supply
> its own slot to return a valid enum value to satisfy the common code.

Sorry, but I still don't follow this. The DT code doesn't use the fixmap,
does it? It looks like it maps the buffer ahead of time using
devm_ioremap_resource() and then the accessors don't use the fixmap
index at all, hence the horrible '(void)fixmap_idx;' cast which presumably
stops the compiler from complaining about an unused variable.

Will