linux-kernel - Re: [PATCH V6 0/6] coresight: etm4x: Migrate ACPI AMBA devices to platform driver

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Message-ID: <e15a4a99-6fda-6f03-3ffb-3db93d678b2c@os.amperecomputing.com>
Date:   Wed, 26 Jul 2023 17:03:32 +0000
From:   Steve Clevenger OS <scclevenger@...amperecomputing.com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        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>,
        "rafael@...nel.org" <rafael@...nel.org>
CC:     Ganapatrao Kulkarni OS <gankulkarni@...amperecomputing.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Len Brown <lenb@...nel.org>,
        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>
Subject: Re: [PATCH V6 0/6] coresight: etm4x: Migrate ACPI AMBA devices to
 platform driver


Hi Suzuki,

On 7/26/2023 9:59 AM, Suzuki K Poulose wrote:
> On 10/07/2023 07:24, Anshuman Khandual wrote:
>> CoreSight ETM4x devices could be accessed either via MMIO (handled via
>> amba_driver) or CPU system instructions (handled via platform driver).
>> But
>> this has the following issues :
>>
>>    - Each new CPU comes up with its own PID and thus we need to keep on
>>      adding the "known" PIDs to get it working with AMBA driver. While
>>      the ETM4 architecture (and CoreSight architecture) defines way to
>>      identify a device as ETM4. Thus older kernels  won't be able to
>>      "discover" a newer CPU, unless we add the PIDs.
>>
>>    - With ACPI, the ETM4x devices have the same HID to identify the
>> device
>>      irrespective of the mode of access. This creates a problem where two
>>      different drivers (both AMBA based driver and platform driver) would
>>      hook into the "HID" and could conflict. e.g., if AMBA driver gets
>>      hold of a non-MMIO device, the probe fails. If we have single driver
>>      hooked into the given "HID", we could handle them seamlessly,
>>      irrespective of the mode of access.
>>
>>    - CoreSight is heavily dependent on the runtime power management. With
>>      ACPI, amba_driver doesn't get us anywhere with handling the power
>>      and thus one need to always turn the power ON to use them. Moving to
>>      platform driver gives us the power management for free.
>>
>> Due to all of the above, we are moving ACPI MMIO based etm4x devices
>> to be
>> supported via tha platform driver. The series makes the existing platform
>> driver generic to handle both type of the access modes. Although existing
>> AMBA driver would still continue to support DT based etm4x MMIO devices.
>> Although some problems still remain, such as manually adding PIDs for all
>> new AMBA DT based devices.
>>
>> The series applies on 6.5-rc1.
>>
>> Changes in V6:
>>
>> - Rebased on 6.5-rc1
>>
> 
> I have queued this version for v6.6, should appear on coresight/next soon.
> 
> Suzuki

Is there anyway to queue this for 6.5? Or has that ship sailed?

Thanks,

Steve C.