linux-kernel - Re: [PATCH v2 7/9] coresight: Consolidate clock enabling

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Message-ID: <20250506105352.GE177796@e132581.arm.com>
Date: Tue, 6 May 2025 11:53:52 +0100
From: Leo Yan <leo.yan@....com>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: Suzuki K Poulose <suzuki.poulose@....com>,
	Mike Leach <mike.leach@...aro.org>,
	James Clark <james.clark@...aro.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v2 7/9] coresight: Consolidate clock enabling

On Mon, May 05, 2025 at 12:58:06PM +0530, Anshuman Khandual wrote:

[...]

> > --- a/drivers/hwtracing/coresight/coresight-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-core.c
> > @@ -1645,6 +1645,51 @@ int coresight_etm_get_trace_id(struct coresight_device *csdev, enum cs_mode mode
> >  }
> >  EXPORT_SYMBOL_GPL(coresight_etm_get_trace_id);
> >  
> > +/*
> > + * Attempt to find and enable programming clock (pclk) and trace clock (atclk)
> > + * for the given device.
> > + *
> > + * The AMBA bus driver will cover the pclk, to avoid duplicate operations,
> > + * skip to get and enable the pclk for an AMBA device.
> > + *
> > + * atclk is an optional clock, it will be only enabled when it is existed.
> > + * Otherwise, a NULL pointer will be returned to caller.
> > + *
> > + * Returns: '0' on Success; Error code otherwise.
> > + */
> > +int coresight_get_enable_clocks(struct device *dev, struct clk **pclk,
> > +				struct clk **atclk)
> 
> These arguments probably could be arranged better as pclk and atclk are
> always contained inside 'xxx_drvdata' structure, which could be derived
> from the 'dev' structure itself, if [dev|platform]_set_drvdata() always
> ensured to be called earlier.

Seems to me, the conclusion "pclk and atclk ... could be derived from
the 'dev' structure itself" is not true.

The reason is the coresight_get_enable_clocks() function is located in
the CoreSight core layer, it has no knowledge for driver data
definitions (see etmv4_drvdata, funnel_drvdata, etc).  as a result, it
cannot directly access the fields "drvdata->pclk" and "drvdata->atclk".

> Currently there are only two instances where a NULL is being passed to
> indicate that 'atclk' clock is not to be probed or enabled. Could not
> individual clock requirements be passed in a flag argument instead ?
> 
> #define CORESIGHT_ENABLE_PCLK	0x1
> #define CORESIGHT_ENABLE_ATCLK	0x2
> 
> coresight_get_enable_clocks(struct device *dev, unsigned long flags)
> 
> - atclk/pclk derived from drdvata which in turn from dev
> - flags can be checked for pclk/atclk requirements
> 
> Even better - as atlck is the only optional clock here, it could just
> have a boolean flag argument to indicate for atclk clock.
>
> > +{
> > +	WARN_ON(!pclk);
> > +
> > +	if (!dev_is_amba(dev)) {
> > +		/*
> > +		 * "apb_pclk" is the default clock name for an Arm Primecell
> > +		 * peripheral, while "apb" is used only by the CTCU driver.
> > +		 *
> > +		 * For easier maintenance, CoreSight drivers should use
> > +		 * "apb_pclk" as the programming clock name.
> > +		 */
> > +		*pclk = devm_clk_get_enabled(dev, "apb_pclk");
> > +		if (IS_ERR(*pclk))
> > +			*pclk = devm_clk_get_enabled(dev, "apb");
> > +		if (IS_ERR(*pclk))
> > +			return PTR_ERR(*pclk);
> > +	} else {
> > +		/* Don't enable pclk for an AMBA device */
> > +		*pclk = NULL;
> > +	}
> 
> Might be better to invert this conditional check as if (dev_is_amba(dev))
> for better readability.

Will refine code for this.

Thanks,
Leo