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Date:   Tue, 22 Jan 2019 20:12:27 +0000
From:   Suzuki K Poulose <>
Subject: Re: [PATCHv4 1/4] arm64: dts: qcom: sdm845: Add Coresight support

Hi Sai,

On 01/22/2019 04:48 PM, Sai Prakash Ranjan wrote:
> Hi Suzuki,
> On 1/22/2019 9:38 PM, Suzuki K Poulose wrote:
>> By inconsistent, I meant the registers provides values which are not
>> the same on two different CPUs of the *same type*. And it is expected
>> that two different CPU/ETM implementations will have different PIDs.
> SDM845 has 4 Kryo 385 Gold (ARM A75) + 4 Kryo 385 Silver (ARM A55),
> so the PID values should be same for 4 ETMs atleast. But here one
> pid value(001bb803) is same for 6 ETMs and other one for 2
> ETMs(001bb802) which seems odd and hence the doubt if these pids
> are even valid ones.

Have you checked other SoCs with A55 for the ETM PID ? The drivers
usually only care about PID0[7-0], PID1[7-0], PID2[3-0] and ignores
the other fields that may change over revisions of the core. So, in your
case the ETM ID could be treated as 0xbb802 and 0xbb803.

>>> 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)

So thats 4 CPUs with 0x1bb803.

>>> [    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.
>> They differ because they are two different types of CPU cores (and 
>> thus different ETM PIDs). What does the Register descriptions say for
>> the Cores ?
>> To me it looks like there are two different types of Qualcomm
>> Cores with their respective ETMs which are missing in the ETM4x
>> driver and we are trying to "make the ETM" work by faking it as
>> something else, which is not nice. I would rather prefer
>> to add the appropriate masks and the expected value for these
>> two different ETM implementations and be done with it, instead
>> of faking it in all the DTs where these cores appear.
> ETM4x driver does not have entries for A55 and A75. Could you please
> let me know the PIDs for these CPUs so that we can compare?

FWIW, here is the PID list:

A75: 0xB_BD_0A
A55: 0xB_BD_05

Btw, I am not sure if the ETM has been changed/tuned for the Cores in
SDM845. Please could you get this clarified internally within your
organisation ?

>>> For MSM8996:
>>> resname=etm@...0000 pid=102f0205
>> I don't know what CPUs the MSM8996 have. If they don't have A53, you
>> must add the actual PIDs to the table once and for all.
> But again, this PID is some invalid value. And does not correspond
> to any of the ARM CPU cores and would be MSM8996 specific.
> MSM8996 has 2+2 Kryo cores which are not ARM derivative as SDM845
> if I am right.

As long as the JEP106 coding standard is followed and is indicated in
the appropriate fields (PIDR2[3]), we should be fine. In the case above:
PID of the ETM is 0xf0205, implies JEP106 code[6:0] of the designer is 
0x70 and ETM part number is : 0x205, which makes sense to me.

>>>>> +        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.
>> There is no measure for "correctness" here. If the ETM exposes different
>> PID than what you expect from the TRM, then we could think of overriding
>> it. Otherwise please add the PIDs to the table.
> This is exactly the case, ETM PID registers are exposing some invalid
> value and hence we override in DT.

It would be good to have this clarified. I will check with the internal
teams here for any details.


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