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Date:   Tue, 22 Jan 2019 20:32:51 +0530
From:   Sai Prakash Ranjan <>
To:     Suzuki K Poulose <>,,,,,,,,,,,,
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 <>
> 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.


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