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

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On 09/01/2025 12:01, Yeoreum Yun wrote:

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Hi Suzuki,

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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

But, when separate the config, it doesn't show anymore the current
configuration set by perf.
I'm not sure this is okay.
IMHO, If perf is enabled, since the configuration show the "perf",
I think prohabit to modify config via sysfs while PERF_ENABLE seems valid.

and about lossing session, I think this is up to user.
That means to use sysfs, user shouldn't use perf to prevent loss
its configuration.

Am I missing something?

Thanks

And one more question.
When CS_SYSFS_ENABLE,  Is it valid to allow modification of "config"?
I think It seems valid to show the "current working configration".
If It allows to modificaiton the config value showed via sysfs and current applied be different.

So, IMHO, It seems to valid to modify "config" only in CS_DISABLED.

Am I missing something?

Thanks.