[PATCH v5 09/11] coresight: etm4x: Add flag to control single-shot restart

[Suzuki K Poulose]

On 11/11/2025 09:24, Leo Yan wrote:
> On Mon, Nov 10, 2025 at 11:37:52AM +0000, Suzuki Kuruppassery Poulose wrote:
> 
> [...]
> 
>>> -static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
>>> +static int etm4_enable_hw(struct etmv4_drvdata *drvdata, bool restart_ss)
>>
>> While this looks to work, I wonder if we could manage this all in the config
>> ? i.e.,
>>
>> Use an extra field, say config->retain_single_shot_status, which defaults to
>> 0 and is always cleared once we pass through enable_hw.
> 
> This is fine for me in general.  I agree that adding an argument in
> etm4_enable_hw() is not scalable, though we can take a bit advantage
> of stack push and pop so no need cleanup.
> 
> Before proceed, I would check another idea.  Can we do this with
> is_idle_task()?
> 
>    if (!is_idle_task(current)) {
>        if (config->ss_ctrl[i] || config->ss_pe_cmp[i])
>            config->ss_status[i] &= ~TRCSSCSRn_STATUS;
>    }

What happens when we do a system wide session and a CPU is running an
idle task ?

Suzuki

> 
> As a result, we can avoid new flag and extra operatoins (set/clear) for
> the added flag.
> 
> Note, this does not only impact CPU idle flow, this also applies on CPU
> hotplug flow (as CPU hotplug callback also runs in idle thread).  I
> think this would be fine, no matter CPU idle or hotplug, we keep the
> single-shot state after the CPU resume back.


> 
> Thoughts?
> 
> Thanks,
> Leo