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Subject: Re: [PATCHv8 2/5] arm64: dts: qcom: msm8998: Add Coresight support
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From:   Suzuki K Poulose <suzuki.poulose@arm.com>
Message-ID: <281e3548-af53-f9a7-b9e4-813b448ab078@arm.com>
Date:   Thu, 18 Jul 2019 10:37:19 +0100
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On 18/07/2019 10:14, Sai Prakash Ranjan wrote:
> Hi Suzuki,
> 
> On 7/18/2019 1:58 PM, Suzuki K Poulose wrote:
>> Hi Sai,
>>
>>
>>           etr@6048000 {
>>> +            compatible = "arm,coresight-tmc", "arm,primecell";
>>> +            reg = <0x06048000 0x1000>;
>>> +
>>> +            clocks = <&rpmcc RPM_SMD_QDSS_CLK>, <&rpmcc
>>> RPM_SMD_QDSS_A_CLK>;
>>> +            clock-names = "apb_pclk", "atclk";
>>> +            arm,scatter-gather;
>>
>> Please could you confirm that you have tested the scatter-gather mode
>> with ETR ? Either via perf/sysfs. Please could you share your results ?
>> Unless verified
>> this is going to be fatal for the system.
>>
>> Similarly for other platforms.
>>
> 
> Yes I have tested with scatter-gather mode with ETR on all platforms
> which I have posted via sysfs(not perf) before on previous versions of
> this patch series and no issues were found. And I suppose this was
> discussed in v2 of this patch series [1].

Using the sysfs doesn't guarantee that the ETR actually uses SG mode, unless
the buffer size selected is > 1M, which is why I am more interested in the
perf usage. Alternatively you may configure a larger buffer size (say, 8MB) via:

echo 0x800000 > /sys/bus/coresight/.../tmc_etr0/buffer_size


> 
> As said in one of the series initially [1], QCOM msm downstream kernels
> have been using scatter gather mode and we haven't seen any fatal issues.
> 
> [1] https://patchwork.kernel.org/patch/10769535/

I haven't seen any test results there either.

Cheers
Suzuki