Re: [PATCHv8 2/5] arm64: dts: qcom: msm8998: Add Coresight support

From: Suzuki K Poulose <suzuki.poulose@arm.com>
To: saiprakash.ranjan@codeaurora.org, gregkh@linuxfoundation.org,
	mathieu.poirier@linaro.org, leo.yan@linaro.org,
	alexander.shishkin@linux.intel.com, mike.leach@linaro.org,
	robh+dt@kernel.org, bjorn.andersson@linaro.org,
	devicetree@vger.kernel.org, david.brown@linaro.org,
	mark.rutland@arm.com
Cc: rnayak@codeaurora.org, vivek.gautam@codeaurora.org,
	sibis@codeaurora.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	marc.w.gonzalez@free.fr
Subject: Re: [PATCHv8 2/5] arm64: dts: qcom: msm8998: Add Coresight support
Date: Thu, 18 Jul 2019 10:37:19 +0100	[thread overview]
Message-ID: <281e3548-af53-f9a7-b9e4-813b448ab078@arm.com> (raw)
In-Reply-To: <4854b0f7-6a81-bc87-3e63-d2b7c68a44f6@codeaurora.org>

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