linux-kernel - Re: [Question] Question about supporting sysreg only CoreSight ETMv4.4 on ACPI machines

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Message-ID: <07c9964b-e074-fe76-8ee1-9b0bdf5d364f@arm.com>
Date:   Thu, 20 Oct 2022 17:03:47 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Xiongfeng Wang <wangxiongfeng2@...wei.com>
Cc:     yehaiyang2@...ilicon.com, wanghuiqiang <wanghuiqiang@...wei.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>, mark.rutland@....com,
        Catalin Marinas <catalin.marinas@....com>,
        Anshuman Khandual <Anshuman.Khandual@....com>
Subject: Re: [Question] Question about supporting sysreg only CoreSight
 ETMv4.4 on ACPI machines

Hi

On 19/10/2022 03:04, Xiongfeng Wang wrote:
> Hi, Suzuki, Anshuman
> 
> On 2022/10/18 17:18, Suzuki Kuruppassery Poulose wrote:
>> Hi,
>>
>> Cc: Anshuman
>>
>> On 18/10/2022 03:04, Xiongfeng Wang wrote:
>>> Hi, Suzuki
>>>
>>>      We are testing CoreSight ETMv4.4 and TRBE recently. ETMv4.4 obsoletes memory
>>> mapped access to ETM and mandates the system registers. The following commit add
>>> driver for sysreg only devices, but it only support device tree.
>>>     commit 5214b563588e8414193bd7a174c52350256942a6
>>>     coresight: etm4x: Add support for sysreg only devices
>>>
>>> ACPI machine can use 'ARMHC500' to report a ETM4x device. But the corresponding
>>> driver is etm4x_amba_driver. It needs memory resouces and doesn't support sysreg
>>> only device.
>>
>> That is true. Unfortunately, supporting this requires us to move away from the
>> AMBA framework (at least) for ETM4x devices. This is currently
>> developed by Anshuman. We can share it as soon as this is complete.
> 
> Thanks a lot. Really appreciate !
> By the way, do we have plan to add ACPI support for TRBE driver? ACPI 6.5 add a

Yes, this is again in our pipeline. But, without the ETE support, TRBE
is literally unusable. So, this will follow the ETE/ETMv4 sysreg ACPI
support.


> field 'TRBE Interrupt' in GICC Structure. In the beginning, I plan to add a
> platform device when got this IRQ, just like what SPE does in the following commit
>    commit d24a0c7099b32b6981d7f126c45348e381718350
>    arm_pmu: acpi: spe: Add initial MADT/SPE probing



> But it seems that TRBE still needs _DSD method to report the links(input port
> and output port). Do you have some other advices? Thanks a lot.

TRBE doesn't need to specify the input/output ports. It is a per-CPU
sink and the TRBE driver registers it as such for each CPU that it
probes.

Suzuki