linux-kernel - Re: [PATCH v5 09/19] arch_topology: Use the last level cache information from the cacheinfo

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Message-ID: <20220629183348.ga7gbcsba57dzf2t@bogus>
Date:   Wed, 29 Jun 2022 19:33:48 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Conor.Dooley@...rochip.com
Cc:     linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
        atishp@...shpatra.org, atishp@...osinc.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        wangqing@...o.com, robh+dt@...nel.org, rafael@...nel.org,
        ionela.voinescu@....com, pierre.gondois@....com,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, gshan@...hat.com,
        Valentina.FernandezAlanis@...rochip.com
Subject: Re: [PATCH v5 09/19] arch_topology: Use the last level cache
 information from the cacheinfo

On Wed, Jun 29, 2022 at 06:18:25PM +0000, Conor.Dooley@...rochip.com wrote:
> On 29/06/2022 18:49, Conor.Dooley@...rochip.com wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > 
> > On 27/06/2022 17:50, Sudeep Holla wrote:
> >> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> >>
> >> The cacheinfo is now initialised early along with the CPU topology
> >> initialisation. Instead of relying on the LLC ID information parsed
> >> separately only with ACPI PPTT elsewhere, migrate to use the similar
> >> information from the cacheinfo.
> >>
> >> This is generic for both DT and ACPI systems. The ACPI LLC ID information
> >> parsed separately can now be removed from arch specific code.
> > 
> > Hey Sudeep,
> > I bisected broken boot on PolarFire SoC to this patch in next-20220629 :/
> > I suspect the issue is a missing "next-level-cache" in the the dt:
> > arch/riscv/boot/dts/microchip/mpfs.dtsi
> > 
> > Adding next-level-cache = <&cctrllr> fixes the boot.
>

If the above is missing, even the existing cacheinfo will be incorrect on
that system. But we must end up with L1 as LLC, I need to check if that
breaks the boot.

> No, no it doesn't. Not sure what I was thinking there.
> Prob tested that on the the last commit that bisect tested
> rather than the one it pointed out the problem was with.
>

So can I assume the pointed commit is where the boot breaks ?

> Either way, boot is broken in -next.
>

OK, that's bad. 

> > Not sure what the resolution here is, old devicetrees are meant to keep
> > booting, right?
> >

Ideally yes. But with this, I assume the cacheinfo to userspace is also broken
on this platform and I guess that needs fixing which can happen with DT update
only.

--
Regards,
Sudeep