Re: Enquiry on Using sysFS for Coresight on Android

Dear Sirs,

My apologies for the late reply.

Much thanks for all the assistance and kind explanation!

Yours Sincerely, Jeremy ________________________________ From: Suzuki K Poulose suzuki.poulose@arm.com Sent: 07 June 2019 19:04 To: Student - Ng Yi Zher Jeremy; mathieu.poirier@linaro.org Cc: coresight@lists.linaro.org Subject: Re: Enquiry on Using sysFS for Coresight on Android

On 07/06/2019 08:04, Student - Ng Yi Zher Jeremy wrote:

Hi Sir,

Thank you for your prompt reply.

Please CC the coresight mailing list when asking questions.

My sincerest apologies for not following the protocols.

> Looking at the documentations for etm4x and tmc (<https://outlook.office.com/mail/inbox/id/AAQkADA5Mzc3ZWFlLWY1MzItNDhiOS1iZmRkLWI2NTE1NWNlM2RlZQAQACr6RgSGfxZKoiPE7yQIcBQ%3D>https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-bus-coresight-devices-etm4x
and
https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-bus-coresight-devices-tmc
respectively), I understand that the special files that I have access to
read from registers directly are not writeable. However, in the coresight
documentations,

What special files are you referring to?

I was referring to the filesystem's special files that give us read (and some write) access to the registers (i.e. the files in /sys/bus/coresight/devices)

Register TRCCONFIGR has been set as RO because, from sysfs, there was
no use case to make it otherwise.  That can be altered if you need to
use some of the functionality in that register.  Simply get back to me
with the one you're looking for and we can discuss how it will be made
available.

1. I will like to activate DA ,DV and COND. I understand that these 2 bits depend on TRCCONFIGR.INSTP0 while this depends on TRCIDR0.INSTP0. Unfortunately, TRCIDR0.INSTP0 is 0b00 in my case. is there any way to work around this to activate data traces?

Arm v8-A ETM implementations do not support Data trace unfortunately. And the TRCIDR0 is a read only register describing the hardware features.

1) You cannot write anything to it. 2) Even if you managed to write, it will not enable data tracing.

2. The reason for wanting to activate data traces is to look at my program instructions and determine, at a hardware level, for any bugs that might have been attributed to hardware bugs.

You may use instruction trace to debug your program, but not the data trace on an armv8-A core.

Cheers Suzuki

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