linux-kernel - Re: [BUG] CoreSight: WARN_ON in coresight_disclaim_device_unlocked due to register reset on CPU power-cycle

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Message-ID: <5428619b-db7c-4b5b-964d-1466e516c245@linaro.org>
Date: Mon, 23 Jun 2025 13:05:13 +0100
From: James Clark <james.clark@...aro.org>
To: Keita Morisaki <keyz@...gle.com>, suzuki.poulose@....com,
 Leo Yan <leo.yan@....com>
Cc: alexander.shishkin@...ux.intel.com, coresight@...ts.linaro.org,
 ericchancf@...gle.com, linux-kernel@...r.kernel.org, mike.leach@...aro.org,
 yimingtseng@...gle.com
Subject: Re: [BUG] CoreSight: WARN_ON in coresight_disclaim_device_unlocked
 due to register reset on CPU power-cycle



On 23/06/2025 9:59 am, Keita Morisaki wrote:
>> We have the ETM driver performing the save/restore of ETM context during
>> a CPUidle. This is only done when the ETM/ETE is described to be loosing
>> context over PM operation. If this is not done (via DT), the driver
>> doesn't do anything. This could be problematic. Could you try adding:
>>
>> "arm,coresight-loses-context-with-cpu"
>>
>>
>> property to the ETE nodes and see if it makes a difference ?
> 
> I tried this in our environment, and this worked well. The "arm,coresight-loses-context-with-cpu" property was what we needed.
> Thank you so much again for the swift response with the useful information!
> 
> Best,
> Keita


Hi Keita,

Thanks for the report. We discussed internally and decided that it would 
be better for the driver to always save the context by default, because 
this mistake is easy to make. Saving when it doesn't need to be saved 
doesn't do any harm, but not saving when it should be causes quite bad bugs.

So "arm,coresight-loses-context-with-cpu" will be ignored in the future 
and we'll add a new flag like "arm,coresight-save-context" if anyone 
wants the optimization of not saving.

Thanks
James