linux-kernel - Re: [PATCHv4 1/4] arm64: dts: qcom: sdm845: Add Coresight support

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Date:   Tue, 22 Jan 2019 20:32:51 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>, robh+dt@...nel.org,
        mathieu.poirier@...aro.org, leo.yan@...aro.org,
        alexander.shishkin@...ux.intel.com, andy.gross@...aro.org,
        david.brown@...aro.org, vivek.gautam@...eaurora.org,
        dianders@...omium.org, sboyd@...nel.org,
        bjorn.andersson@...aro.org, devicetree@...r.kernel.org,
        mark.rutland@....com
Cc:     rnayak@...eaurora.org, sibis@...eaurora.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCHv4 1/4] arm64: dts: qcom: sdm845: Add Coresight support

Hi Suzuki,

Thanks for looking into this. Please find my response inline.

On 1/22/2019 7:30 PM, Suzuki K Poulose wrote:
> Hi Sai,
> 
> On 01/22/2019 01:37 PM, Sai Prakash Ranjan wrote:
>> Add coresight components found on Qualcomm SDM845 SoC.
>>
>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
>>
> 
> Sorry, but I hadn't noticed the PID override strings below. Please
> find the question.
>
[..]

>> +        /*
>> +         * On QCOM SDM845, we bypass the normal AMBA bus discovery
>> +         * method by forcing the peripheral ID because of the wrong
>> +         * value read from ETM PID registers.
>> +         */
> 
> What is the value read back from the ETM PIDx registers ? Do they
> provide inconsistent or incompatible value w.r.t the ETM/Coresight
> architecture ? If it is an unsupported CPU with proper values,
> you must add them to the table in etm4x driver.
> 

The values read from ETM PIDx registers are actually inconsistent
and is different for some ETMs.

Below are the PIDs read for SDM845:

[    5.996448] resname=etm@...0000 pid=001bb803
[    6.052891] resname=etm@...0000 pid=001bb803

<snip> .. (Same pid=001bb803 for etm@...0000 to etm@...0000 but differs
for other 2 cpus as shown below)

[    6.266687] resname=etm@...0000 pid=001bb802
[    6.329171] resname=etm@...0000 pid=001bb802

This is the case for MSM8996 also as shown below where PID
value is not correct and has to be hardcoded.

For MSM8996:

resname=etm@...0000 pid=102f0205

>> +        etm@...0000 {
>> +            compatible = "arm,coresight-etm4x", "arm,primecell";
>> +            arm,primecell-periphid = <0x000bb95d> > +            reg 
>> = <0 0x07040000 0 0x1000>;
>> +
>> +            cpu = <&CPU0>;
>> +
> 
> You seem to be specifying the PID of A53 ETM all over, while at least
> one of your cores is ETMv4.2 (from the other patch) and A53 is not
> ETMv4.2. As above, it would be good to add the PID to the table.
> 

As explained in above comment, PID values read are not correct. Please 
let me know if I am not clear.

Thanks,
Sai

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