Re: [PATCH 1/2] dt-bindings: edac: Add DT bindings for Kryo EDAC

[Sai Prakash Ranjan]

Hi James,

On 2020-01-16 00:18, James Morse wrote:
> Hi Sai,
>
> (CC: +Tyler)
>
> On 05/12/2019 09:53, Sai Prakash Ranjan wrote:
> > This adds DT bindings for Kryo EDAC implemented with RAS
> > extensions on KRYO{3,4}XX CPU cores for reporting of cache
> > errors.
>
> KRYO{3,4}XX isn't the only SoC with the RAS extensions. The DT needs
> to convey the range
> of ways this armv8 RAS extensions stuff can be wired up.

Right, but I was going for Kryo specific implementation and hence the 
binding as such.

> The folk who look after the ACPI specs have made a start:
> https://static.docs.arm.com/den0085/a/DEN0085_RAS_ACPI_1.0_BETA_1.pdf
>
> (I suspect that isn't the latest version, I'll try and find out)

That would be helpful, thanks.

> I'd like the ACPI table and DT to convey the same information so that
> we don't need to
> convert or infer things in the driver. If something is missing, we
> should get it added!

Sure, I think it is decided now that kernel first RAS implementation 
will be generic.

> > diff --git 
> > a/Documentation/devicetree/bindings/edac/qcom-kryo-edac.yaml 
> > b/Documentation/devicetree/bindings/edac/qcom-kryo-edac.yaml
> > new file mode 100644
> > index 000000000000..1a39429a73b4
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/edac/qcom-kryo-edac.yaml
> > @@ -0,0 +1,67 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/edac/qcom-kryo-edac.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Kryo Error Detection and Correction(EDAC)
> > +
> > +maintainers:
> > +  - Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> > +
> > +description: |
> > +  Kryo EDAC is defined to describe on-chip error detection and 
> > correction
> > +  for the Kryo CPU cores which implement RAS extensions.
>
> Please don't make this Kryo specific, otherwise this binding becomes
> an extra thing we
> need to support with a 'v8.2 RAS' driver.
>
> What I'd like is a single 'armv82_ras' edac driver that handles faults
> and errors reported
> by interrupts, and interacts with the arch code's handling of
> 'external aborts'. This
> should work for all platforms using v8.2 RAS and later.

Ok sure.

> > +  It will report
> > +  all Single Bit Errors and Double Bit Errors found in L1/L2 caches 
> > in
> > +  in two registers ERXSTATUS_EL1 and ERXMISC0_EL1. L3-SCU cache 
> > errors
> > +  are reported in ERR1STATUS and ERR1MISC0 registers.
> > +    ERXSTATUS_EL1 - Selected Error Record Primary Status Register, 
> > EL1
> > +    ERXMISC0_EL1 - Selected Error Record Miscellaneous Register 0, 
> > EL1
> > +    ERR1STATUS - Error Record Primary Status Register
> > +    ERR1MISC0 - Error Record Miscellaneous Register 0
> > +  Current implementation of Kryo ECC(Error Correcting Code) mechanism 
> > is
> > +  based on interrupts.
>
> Your SoC picked the system registers as the interface to these
> component's registers.
> The binding would need to specify which index the 'l1-l2' records
> start at, and how many
> there are. The same for the 'l3-scu'. You can't hard code these, they
> are different on
> other platforms.

Ok will keep this in mind for the next version.

> There is also an MMIO interface which needs a base address, along with
> the index and
> ranges. (which may be different). The same component may use both the
> system register and
> the MMIO interface.

I have some doubts here, Where do I get this info? Will this be 
implementation specific?

> This stuff is likely to vary on big/little systems, so you need a way
> of describing which
> CPUs the settings refer to. This probably isn't something the ACPI
> tables capture as ACPI
> machines are typically homogenous.

Our SoCs are based on big.LITTLE arch, so this will be needed.

Thanks,
Sai

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