linux-kernel - Re: [PATCH 1/3] arm64: dts: qcom: sdm845: Add Coresight support

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Date:   Tue, 15 Jan 2019 21:59:11 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Brown <david.brown@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Sibi Sankar <sibis@...eaurora.org>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Leo Yan <leo.yan@...aro.org>,
        Andy Gross <andy.gross@...aro.org>,
        linux-arm-msm-owner@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] arm64: dts: qcom: sdm845: Add Coresight support

Hi Mathieu,

On 1/14/2019 9:05 PM, Mathieu Poirier wrote:
> On Sat, Jan 12, 2019 at 06:21:00PM +0530, saiprakash.ranjan@...eaurora.org wrote:
>> Hi Mathieu,
>>
>>>> +
>>>> +	etm@...0000 {
>>>> +		compatible = "arm,coresight-etm4x", "arm,primecell";
>>>> +		arm,primecell-periphid = <0x000bb95d>;
>>>
>>> I'm a little curious as to why you need to bypass the normal AMBA bus
>>> discovery
>>> method by forcing the peripheral ID.  Tracers don't show up the way
>>> other
>>> coresight devices do at boot time?
>>>
>>
>> Yes on some Qcom SoC's like SDM845 and also on some previous ones, for
>> ETM(only) amba bus discovery method fails because of wrong pid read from the
>> registers. So we have to force this primecell peripheral ids to probe etm.
> 
> Ok, if that is the case please add a comment to explain the situation.
> Otherwise someone will assuredly ask again in the future.
> 

Sure, will add it in the next version.

Thanks,
Sai

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