linux-kernel - Re: [PATCH v6 01/20] clk: bump stdout clock usage for earlycon

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Message-ID: <d4580b33c195dcf1c3a0054b29555383d2e1606b.camel@linaro.org>
Date: Fri, 09 Aug 2024 10:02:25 +0100
From: André Draszik <andre.draszik@...aro.org>
To: Peng Fan <peng.fan@....com>, Michael Turquette
 <mturquette@...libre.com>,  Stephen Boyd <sboyd@...nel.org>, Peter Griffin
 <peter.griffin@...aro.org>, Krzysztof Kozlowski <krzk@...nel.org>,
 Sylwester Nawrocki <s.nawrocki@...sung.com>, Chanwoo Choi
 <cw00.choi@...sung.com>, Alim Akhtar <alim.akhtar@...sung.com>, Sam
 Protsenko <semen.protsenko@...aro.org>, Tudor Ambarus
 <tudor.ambarus@...aro.org>, Abel Vesa <abelvesa@...nel.org>, Shawn Guo
 <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix
 Kernel Team <kernel@...gutronix.de>,  Fabio Estevam <festevam@...il.com>
Cc: Will McVicker <willmcvicker@...gle.com>, "kernel-team@...roid.com"
 <kernel-team@...roid.com>, "linux-clk@...r.kernel.org"
 <linux-clk@...r.kernel.org>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
 <linux-arm-kernel@...ts.infradead.org>, "linux-samsung-soc@...r.kernel.org"
 <linux-samsung-soc@...r.kernel.org>, "imx@...ts.linux.dev"
 <imx@...ts.linux.dev>
Subject: Re: [PATCH v6 01/20] clk: bump stdout clock usage for earlycon

Hi Peng,

On Fri, 2024-08-09 at 07:16 +0000, Peng Fan wrote:
> > +static int __init of_clk_drop_stdout_clocks(void) {
> > +	for (size_t i = 0; i < of_clk_stdout_clks.n_clks; ++i) {
> > +		clk_disable_unprepare(of_clk_stdout_clks.clks[i]);
> > +		clk_put(of_clk_stdout_clks.clks[i]);
> > +	}
> > +
> > +	kfree(of_clk_stdout_clks.clks);
> > +
> > +	/*
> > +	 * Do not try to acquire stdout clocks after late initcalls, e.g.
> > +	 * during further module loading, as we then wouldn't have a
> > way to
> > +	 * drop the references (and associated allocations) ever again.
> > +	 */
> > +	of_clk_stdout_clks.bump_refs = false;
> > +
> > +	return 0;
> > +}
> > +late_initcall_sync(of_clk_drop_stdout_clocks);
> 
> If the uart driver is built as module, this might break earlycon.
> Before uart driver loaded, clk disabled per my understanding.

You're right.

With this in mind, I'm not sure then if a generic solution is possible...

I guess it has to be duplicated into the platforms after all and platforms
can enable this if they opt to disallow uart as module?

Any other suggestions?

> > +
> >  /**
> >   * struct of_clk_provider - Clock provider registration structure
> >   * @link: Entry in global list of clock providers @@ -5031,6 +5156,8
> > @@ int of_clk_add_provider(struct device_node *np,
> > 
> >  	fwnode_dev_initialized(&np->fwnode, true);
> > 
> > +	of_clk_bump_stdout_clocks();
> > +
> >  	return ret;
> >  }
> >  EXPORT_SYMBOL_GPL(of_clk_add_provider);
> > @@ -5073,6 +5200,8 @@ int of_clk_add_hw_provider(struct
> > device_node *np,
> > 
> >  	fwnode_dev_initialized(&np->fwnode, true);
> > 
> > +	of_clk_bump_stdout_clocks();
> 
> If clock driver is built as module,  the will make the
> clocks will be always enabled, if my understanding is correct.

until late_initcall_sync(), at which point it'll be disabled before the uart
driver has probed, yes :-(

Cheers,
Andre'