Re: [PATCH 3/8] clk: sunxi: Add a driver for the PLL2

[Maxime Ripard <maxime.ripard@free-electrons.com>]

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On Fri, May 15, 2015 at 05:15:32PM +0800, Chen-Yu Tsai wrote:
> On Fri, May 15, 2015 at 3:45 PM, Maxime Ripard
> <maxime.ripard@free-electrons.com> wrote:
> > On Thu, May 14, 2015 at 05:43:51PM +0800, Chen-Yu Tsai wrote:
> >> Hi,
> >>
> >> On Sat, May 2, 2015 at 7:24 PM, Maxime Ripard
> >> <maxime.ripard@free-electrons.com> wrote:
> >> > The PLL2 on the A10 and later SoCs is the clock used for all the audio
> >> > related operations.
> >> >
> >> > This clock has a somewhat complex output tree, with three outputs (2X, 4X
> >> > and 8X) with a fixed divider from the base clock, and an output (1X) with a
> >> > post divider.
> >> >
> >> > However, we can simplify things since the 1X divider can be fixed, and we
> >> > end up by having a base clock not exposed to any device (or at least
> >> > directly, since the 4X output doesn't have any divider), and 4 fixed
> >> > divider clocks that will be exposed.
> >> >
> >> > This clock seems to have been introduced, at least in this form, in the
> >> > revision B of the A10, but we don't have any information on the clock used
> >> > on the revision A.
> >> >
> >> > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> >> > ---
> >> >  drivers/clk/sunxi/Makefile                 |   1 +
> >> >  drivers/clk/sunxi/clk-a10-pll2.c           | 176 +++++++++++++++++++++++++++++
> >> >  include/dt-bindings/clock/sun4i-a10-pll2.h |  53 +++++++++
> >> >  3 files changed, 230 insertions(+)
> >> >  create mode 100644 drivers/clk/sunxi/clk-a10-pll2.c
> >> >  create mode 100644 include/dt-bindings/clock/sun4i-a10-pll2.h
> >> >
> >> > diff --git a/drivers/clk/sunxi/Makefile b/drivers/clk/sunxi/Makefile
> >> > index 058f273d6154..eb36c38d4120 100644
> >> > --- a/drivers/clk/sunxi/Makefile
> >> > +++ b/drivers/clk/sunxi/Makefile
> >> > @@ -4,6 +4,7 @@
> >> >
> >> >  obj-y += clk-sunxi.o clk-factors.o
> >> >  obj-y += clk-a10-hosc.o
> >> > +obj-y += clk-a10-pll2.o
> >> >  obj-y += clk-a20-gmac.o
> >> >  obj-y += clk-mod0.o
> >> >  obj-y += clk-sun8i-mbus.o
> >> > diff --git a/drivers/clk/sunxi/clk-a10-pll2.c b/drivers/clk/sunxi/clk-a10-pll2.c
> >> > new file mode 100644
> >> > index 000000000000..4d0369626dba
> >> > --- /dev/null
> >> > +++ b/drivers/clk/sunxi/clk-a10-pll2.c
> >> > @@ -0,0 +1,176 @@
> >> > +/*
> >> > + * Copyright 2013 Emilio López
> >> > + * Emilio López <emilio@elopez.com.ar>
> >> > + *
> >> > + * Copyright 2015 Maxime Ripard
> >> > + * Maxime Ripard <maxime.ripard@free-electrons.com>
> >> > + *
> >> > + * This program is free software; you can redistribute it and/or modify
> >> > + * it under the terms of the GNU General Public License as published by
> >> > + * the Free Software Foundation; either version 2 of the License, or
> >> > + * (at your option) any later version.
> >> > + *
> >> > + * This program is distributed in the hope that it will be useful,
> >> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> >> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> >> > + * GNU General Public License for more details.
> >> > + */
> >> > +
> >> > +#include <linux/clk-provider.h>
> >> > +#include <linux/of.h>
> >> > +#include <linux/of_address.h>
> >> > +#include <linux/slab.h>
> >> > +
> >> > +#include <dt-bindings/clock/sun4i-a10-pll2.h>
> >> > +
> >> > +#include "clk-factors.h"
> >> > +
> >> > +#define SUN4I_PLL2_ENABLE              31
> >> > +#define SUN4I_PLL2_POST_DIV            26
> >> > +#define SUN4I_PLL2_POST_DIV_MASK       0xF
> >> > +#define SUN4I_PLL2_N                   8
> >> > +#define SUN4I_PLL2_N_MASK              0x7F
> >> > +#define SUN4I_PLL2_PRE_DIV             0
> >> > +#define SUN4I_PLL2_PRE_DIV_MASK                0x1F
> >> > +
> >> > +#define SUN4I_PLL2_POST_DIV_VALUE      21
> 
> Another thing:
> 
> This says 21, which obviously exceeds the mask defined above,
> but the comment in the section below (in the original code)
> says 4. I assume the comment was right, based on the user
> manual?
> 
> Maybe it should be swapped with SUN4I_PLL2_PRE_DIV_VALUE?
> I get PRE_DIV = 21 for generating a clock close to 22.5792 MHz.

You're right. POST_DIV_VALUE and PRE_DIV_VALUE are inverted....

I wonder how that was even working...

> Seems AC97 might need another frequency, but the manual isn't
> clear, and we can handle it when we add AC97 anyway.

I'm not even sure there's a board out there with an AC97 codec...

> 
> >> > +#define SUN4I_PLL2_PRE_DIV_VALUE       4
> >> > +
> >> > +#define SUN4I_PLL2_OUTPUTS             4
> >> > +
> >> > +static void sun4i_a10_get_pll2_base_factors(u32 *freq, u32 parent_rate,
> >> > +                                           u8 *n, u8 *k, u8 *m, u8 *p)
> >> > +{
> >> > +       /*
> >> > +        * Normalize the frequency to a multiple of (24 MHz / Fixed
> >> > +        * PRE-DIV)
> >> > +        */
> >> > +       *freq = round_down(*freq, parent_rate / SUN4I_PLL2_PRE_DIV_VALUE);
> >> > +
> >> > +       /* We were called to round the frequency, we can return */
> >> > +       if (!n)
> >> > +               return;
> >> > +
> >> > +       *n = *freq * SUN4I_PLL2_PRE_DIV_VALUE / parent_rate;
> >> > +
> >> > +       /*
> >> > +        * Even though the pre-divider can be changed, we don't really
> >> > +        * care and we can just fix it to 4.
> >> > +        */
> >> > +       *m = SUN4I_PLL2_PRE_DIV_VALUE;
> >> > +}
> >> > +
> >> > +static struct clk_factors_config sun4i_a10_pll2_base_config = {
> >> > +       .mshift = SUN4I_PLL2_PRE_DIV,
> >> > +       .mwidth = 5,
> >> > +       .nshift = SUN4I_PLL2_N,
> >> > +       .nwidth = 7,
> >> > +
> >> > +       .m_zero = 1,
> >> > +       .n_zero = 1,
> >> > +};
> >> > +
> >> > +static const struct factors_data sun4i_a10_pll2_base_data __initconst = {
> >> > +       .enable = SUN4I_PLL2_ENABLE,
> >> > +       .table = &sun4i_a10_pll2_base_config,
> >> > +       .getter = sun4i_a10_get_pll2_base_factors,
> >> > +       .name = "pll2-base",
> >> > +};
> >> > +
> >> > +static DEFINE_SPINLOCK(sun4i_a10_pll2_lock);
> >> > +
> >> > +static void __init sun4i_pll2_setup(struct device_node *node)
> >> > +{
> >> > +       const char *clk_name = node->name, *parent;
> >> > +       struct clk_onecell_data *clk_data;
> >> > +       struct clk **clks, *base_clk;
> >> > +       void __iomem *reg;
> >> > +       u32 val;
> >> > +
> >> > +       reg = of_io_request_and_map(node, 0, of_node_full_name(node));
> >> > +       if (IS_ERR(reg))
> >> > +               return;
> >> > +
> >> > +       clk_data = kzalloc(sizeof(*clk_data), GFP_KERNEL);
> >> > +       if (!clk_data)
> >> > +               goto err_unmap;
> >> > +
> >> > +       clks = kcalloc(SUN4I_PLL2_OUTPUTS, sizeof(struct clk *), GFP_KERNEL);
> >> > +       if (!clks)
> >> > +               goto err_free_data;
> >> > +
> >> > +       base_clk = sunxi_factors_register(node, &sun4i_a10_pll2_base_data,
> >> > +                                         &sun4i_a10_pll2_lock, reg);
> >>
> >> Why aren't you using divs_clk for this? It seems right for the job.
> >
> > As far as I know, divs_clk can only handle a single divider, and not
> > two subsequent dividers like this one uses.
> 
> I thought we were setting the post divider to 4 so the outputs match
> the names? Maybe we could get it in as is (with the above comment
> addressed), and refactor it later. I'm still stuck on factors_clk
> stuff....

We are, but the pre-div is considered as the M factor, and the N
factor as N, so we can't really consider it as a single divider.

Thinking a bit more about this, what we could do though, is splitting
the pll2-base clock in half, one that would expose a single divider
using clk-divider for the pre-divider, then a factor clock for the N
factor, and then multiple dividers for the post-divider and other
outputs.

I wonder if that could not even be made that way for all the factors
clock. That would reduce the needed logic in the drivers a lot.

Maxime

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

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