linux-kernel - Re: acpi: Remove ETM from AMBA scan list (was Re: [PATCH V6 6/6] coresight: etm4x: Add ACPI support in platform driver)

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Date:   Wed, 26 Jul 2023 16:33:26 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Steve Clevenger OS <scclevenger@...amperecomputing.com>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Ganapatrao Kulkarni OS <gankulkarni@...amperecomputing.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Sudeep Holla <sudeep.holla@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "coresight@...ts.linaro.org" <coresight@...ts.linaro.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Subject: Re: acpi: Remove ETM from AMBA scan list (was Re: [PATCH V6 6/6]
 coresight: etm4x: Add ACPI support in platform driver)

On Tue, Jul 25, 2023 at 10:18 PM Steve Clevenger OS
<scclevenger@...amperecomputing.com> wrote:
>
>
> Hi Rafael, Len,
>
> On 7/24/2023 9:25 AM, Suzuki K Poulose wrote:
> > Hi Rafael/Len
> >
> > On 19/07/2023 11:11, Suzuki K Poulose wrote:
> >> Rafael, Len
> >>
> >> Ping (packets 6, lost 100%).
> >>
> >>
> >> On 10/07/2023 17:40, Suzuki K Poulose wrote:
> >>> Rafael, Len
> >>>
> >>> On 10/07/2023 07:25, Anshuman Khandual wrote:
> >>>> From: Suzuki K Poulose <suzuki.poulose@....com>
> >>>>
> >>>> Drop ETM4X ACPI ID from the AMBA ACPI device list, and instead just
> >>>> move it
> >>>> inside the new ACPI devices list detected and used via platform driver.
> >>>>
> >>>> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> >>>> Cc: Len Brown <lenb@...nel.org>
> >>>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> >>>> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> >>>> Cc: Mike Leach <mike.leach@...aro.org>
> >>>> Cc: Leo Yan <leo.yan@...aro.org>
> >>>> Cc: Sudeep Holla <sudeep.holla@....com>
> >>>> Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>
> >>>> Cc: linux-acpi@...r.kernel.org
> >>>> Cc: coresight@...ts.linaro.org
> >>>> Cc: linux-arm-kernel@...ts.infradead.org
> >>>> Cc: linux-kernel@...r.kernel.org
> >>>> Reviewed-by: Sudeep Holla <sudeep.holla@....com> (for ACPI specific
> >>>> changes)
> >>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> >>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> >>>
> >>> We would like to queue this via coresight tree. The acpi_amba bits have
> >>> been reviewed by Sudeep. Please could you give us an Ack, if you are
> >>> happy with the proposal ?
> >>>
> >
> > Please could one of you respond to this patch ? We are blocked on your
> > Ack for queuing this. There are machines out there, which rely on this
> > patch to use Arm self-hosted tracing based on CoreSight.
> >
> > Kind regards
> > Suzuki
>
> Ampere Computing AmpereOne machines rely on this patch series to enable
> System Register Access to the ETMv4. Ampere removed the ETM MMIO
> descriptions from our CoreSight ACPI to use this.
>
> Suzuki's e-mail requests for review/Ack of this patch thread date back
> to May 30.

I've just talked to Suzuki about this:

https://lore.kernel.org/linux-acpi/20230726140515.368981-1-suzuki.poulose@arm.com

This patch has received a Reviewed-by from Sudeep which for all
purposes should be sufficient for any ARM-related ACPI material that
doesn't affect any other architectures.  An ACK from me (or Len for
that matter) would not make any real difference from the technical
perspective.

I would appreciate assigning an official ARM maintainer to acpi_amba.c
so as to avoid such unnecessary delays in the future.