[PATCH v6 01/20] clk: bump stdout clock usage for earlycon

[André Draszik]

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'