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

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Message-ID: <1b30a44e-519c-d4d5-ff98-f246cd70fe7c@arm.com>
Date:   Wed, 26 Jul 2023 18:32:55 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Steve Clevenger OS <scclevenger@...amperecomputing.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

On 26/07/2023 18:03, Steve Clevenger OS wrote:
> 
> 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?

Only fixes are allowed for v6.5 at this time.

Suzuki

> 
> Thanks,
> 
> Steve C.