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

On 18/07/2019 10:14, Sai Prakash Ranjan wrote:

Hi Suzuki,

On 7/18/2019 1:58 PM, Suzuki K Poulose wrote:

quoted

Hi Sai,


          etr@6048000 {

quoted

+            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