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

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Date:   Tue, 18 Oct 2022 10:18:08 +0100
From:   Suzuki Kuruppassery 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,

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
Suzuki

> 
> Do we have some other way to use CoreSight ETMv4.4 on ACPI machines. Thanks a lot.
> 
> Thanks,
> Xiongfeng