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

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Message-ID: <Z3/AulnRioAfiSxE@e129823.arm.com>
Date: Thu, 9 Jan 2025 12:27:38 +0000
From: Yeoreum Yun <yeoreum.yun@....com>
To: Suzuki K Poulose <suzuki.poulose@....com>
Cc: mike.leach@...aro.org, james.clark@...aro.org,
	alexander.shishkin@...ux.intel.com, coresight@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] coresight/etm4x: disallow altering config via sysfs
 while enabled

Hi Suzuki,

> 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.
>

I agree. okay. I've posted with separate configuration.
Thanks!