linux-kernel - Re: [PATCH v2 14/15] clk: sunxi-ng: Add H3 clocks

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Message-ID: <20160628083241.GA5550@lukather>
Date:	Tue, 28 Jun 2016 10:32:41 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Michael Turquette <mturquette@...libre.com>
Cc:	Stephen Boyd <sboyd@...eaurora.org>, Chen-Yu Tsai <wens@...e.org>,
	linux-clk@...r.kernel.org, Hans de Goede <hdegoede@...hat.com>,
	Andre Przywara <andre.przywara@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Vishnu Patekar <vishnupatekar0510@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Jean-Francois Moine <moinejf@...e.fr>,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 14/15] clk: sunxi-ng: Add H3 clocks

On Mon, Jun 27, 2016 at 05:53:37PM -0700, Michael Turquette wrote:
> > > The nice thing about struct ccu_common is that you don't have to walk
> > > the list of clocks for each separate clock type like the above probe
> > > function does. I'm still thinking of the best way to solve this
> > > generically. Maybe add a .base member struct clk_hw? I dunno, and I've
> > > resisted the urge to add stuff to struct clk_hw in the past... But I
> > > really want to minimize this .probe as much as possible, and I do not
> > > want every clock provider driver to be forced to invent something like
> > > struct ccu_common every time.
> > 
> > We'd need a few more things (in this case) at least: the register
> > offset and a private field to store our flags.
> 
> A bit of mumbling to myself below:
> 
> Hmm, upon further reflection, walking the list of ccu clocks is rather
> identical to walking the list of each clock type, as I do in the gxbb
> driver, where ccu_common is the one and only clock type.
> 
> So that in itself is not a big deal and isn't a problem that needs
> solving.
> 
> What needs solving is a way to populate base addresses for each clock at
> runtime in a way that does not *force* you to invent something like
> ccu_common if you do not need it.
> 
> You would hit this issue if you broke your common gate or divider clocks
> out and did not wrap them in the ccu_common structure. I solved this by
> overloading the ->reg value of each of the common types as static data,
> and then did the following when registering them:
> 
> 	/* Populate base address for gates */
> 	for (i = 0; i < ARRAY_SIZE(gxbb_clk_gates); i++)
> 		gxbb_clk_gates[i]->reg = clk_base +
> 			(u64)gxbb_clk_gates[i]->reg;
> 
> Any thoughts on how to fix this for other common gate types that need
> their base addresses populated from an OF node at runtime?

One obvious way to work around it would be to allow to store a regmap
directly in the clk_hw structure, and then you'll only need to keep
the register offset in your clock type, which is fine (I think?).

> > > > diff --git a/include/dt-bindings/clock/sun8i-h3.h b/include/dt-bindings/clock/sun8i-h3.h
> > > > new file mode 100644
> > > > index 000000000000..96eced56e7a2
> > > > --- /dev/null
> > > > +++ b/include/dt-bindings/clock/sun8i-h3.h
> > > > @@ -0,0 +1,162 @@
> > > > +#ifndef _DT_BINDINGS_CLK_SUN8I_H3_H_
> > > > +#define _DT_BINDINGS_CLK_SUN8I_H3_H_
> > > > +
> > > > +#define CLK_PLL_CPUX           0
> > > > +#define CLK_PLL_AUDIO_BASE     1
> > > > +#define CLK_PLL_AUDIO          2
> > > > +#define CLK_PLL_AUDIO_2X       3
> > > > +#define CLK_PLL_AUDIO_4X       4
> > > 
> > > Are you sure you want to expose all of these clocks as part of the ABI?
> > > I exposed the bare minimum clocks for the gxbb driver in the DT shared
> > > header (we can always add more later) and kept the rest internal to the
> > > kernel source.
> > 
> > I thought about it, but that would require a third array with
> > basically the same clocks:
> > 
> >   * the ccu_common array to patch to set the lock and base pointers,
> >   * the list of clocks to register
> >   * the clk_hw_onecell_data to deal with the dt binding.
> 
> "the list of clocks to register" and "the clk_hw_onecell_data to deal
> with the dt binding" are the same array.
> 
> You only need two arrays:
> 
> 1) the ccu_common init data
> 2) the clk_hw_onecell_data array of clk_hw pointers that points to
> clk_hw statically defined in the ccu_common array

Ah, so you're still exposing them (anyone could be free to access of
the hidden clocks if it knows what value to use), but you're hiding
them (the ID is not public).

That could work, I'll change that.

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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