Re: [PATCH 1/4] coresight/etm4x: disallow altering config via sysfs while enabled

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 09/01/2025 12:01, Yeoreum Yun wrote:
> Hi Suzuki,
> 
>> Is it not better to have separate "configs" for perf and sysfs ?
>> And etmX driver can populate the "running" config, based on the
>> mode specific config. That way, the configs can be updated
>> independently without affecting the running config or the perf one.
>>
> 
> That was i've tried but I've accepted Mike's opinion that
> it's enough to check whether CS_MODE_DISABLED via coresight_get_mode()
> in *_store().
> 
> "the .._store functions in sysfs should use coresight_get_mode() to ensure
> this is set to CS_MODE_DISABLED before altering the config,
> which ensures that the trace system is inactive.
> We don't' really care about reading the config if trace is running."

There are two issues with that :

1. Sprinkling the get_mode call in each sysfs stor function doesn't look 
good to me.

2. Someone preparing for a sysfs session must not be prevented from 
doing so just because there is a perf session running.


Suzuki


> Thanks.
>