linux-kernel - Re: [linux-sunxi] [PATCH] clk: sunxi-ng: h6: Use sigma-delta modulation for audio PLL

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Date:   Thu, 19 Sep 2019 20:18:37 +0200
From:   Maxime Ripard <mripard@...nel.org>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Jernej Skrabec <jernej.skrabec@...l.net>,
        Mike Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [linux-sunxi] [PATCH] clk: sunxi-ng: h6: Use sigma-delta
 modulation for audio PLL

On Wed, Sep 18, 2019 at 01:46:34PM +0800, Chen-Yu Tsai wrote:
> On Wed, Sep 18, 2019 at 1:21 PM Jernej Škrabec <jernej.skrabec@...l.net> wrote:
> >
> > Dne torek, 17. september 2019 ob 08:54:08 CEST je Chen-Yu Tsai napisal(a):
> > > On Sat, Sep 14, 2019 at 9:51 PM Jernej Skrabec <jernej.skrabec@...l.net>
> > wrote:
> > > > Audio devices needs exact clock rates in order to correctly reproduce
> > > > the sound. Until now, only integer factors were used to configure H6
> > > > audio PLL which resulted in inexact rates. Fix that by adding support
> > > > for fractional factors using sigma-delta modulation look-up table. It
> > > > contains values for two most commonly used audio base frequencies.
> > > >
> > > > Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> > > > ---
> > > >
> > > >  drivers/clk/sunxi-ng/ccu-sun50i-h6.c | 21 +++++++++++++++------
> > > >  1 file changed, 15 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/drivers/clk/sunxi-ng/ccu-sun50i-h6.c
> > > > b/drivers/clk/sunxi-ng/ccu-sun50i-h6.c index d89353a3cdec..ed6338d74474
> > > > 100644
> > > > --- a/drivers/clk/sunxi-ng/ccu-sun50i-h6.c
> > > > +++ b/drivers/clk/sunxi-ng/ccu-sun50i-h6.c
> > > > @@ -203,12 +203,21 @@ static struct ccu_nkmp pll_hsic_clk = {
> > > >
> > > >   * hardcode it to match with the clock names.
> > > >   */
> > > >
> > > >  #define SUN50I_H6_PLL_AUDIO_REG                0x078
> > > >
> > > > +
> > > > +static struct ccu_sdm_setting pll_audio_sdm_table[] = {
> > > > +       { .rate = 541900800, .pattern = 0xc001288d, .m = 1, .n = 22 },
> > > > +       { .rate = 589824000, .pattern = 0xc00126e9, .m = 1, .n = 24 },
> > > > +};
> > > > +
> > > >
> > > >  static struct ccu_nm pll_audio_base_clk = {
> > > >
> > > >         .enable         = BIT(31),
> > > >         .lock           = BIT(28),
> > > >         .n              = _SUNXI_CCU_MULT_MIN(8, 8, 12),
> > > >         .m              = _SUNXI_CCU_DIV(1, 1), /* input divider */
> > > >
> > > > +       .sdm            = _SUNXI_CCU_SDM(pll_audio_sdm_table,
> > > > +                                        BIT(24), 0x178, BIT(31)),
> > > >
> > > >         .common         = {
> > > >
> > > > +               .features       = CCU_FEATURE_SIGMA_DELTA_MOD,
> > > >
> > > >                 .reg            = 0x078,
> > > >                 .hw.init        = CLK_HW_INIT("pll-audio-base", "osc24M",
> > > >
> > > >                                               &ccu_nm_ops,
> > > >
> > > > @@ -753,12 +762,12 @@ static const struct clk_hw *clk_parent_pll_audio[] =
> > > > {>
> > > >  };
> > > >
> > > >  /*
> > > >
> > > > - * The divider of pll-audio is fixed to 8 now, as pll-audio-4x has a
> > > > - * fixed post-divider 2.
> > > > + * The divider of pll-audio is fixed to 24 for now, so 24576000 and
> > > > 22579200 + * rates can be set exactly in conjunction with sigma-delta
> > > > modulation.>
> > > >   */
> > > >
> > > >  static CLK_FIXED_FACTOR_HWS(pll_audio_clk, "pll-audio",
> > > >
> > > >                             clk_parent_pll_audio,
> > > >
> > > > -                           8, 1, CLK_SET_RATE_PARENT);
> > > > +                           24, 1, CLK_SET_RATE_PARENT);
> > > >
> > > >  static CLK_FIXED_FACTOR_HWS(pll_audio_2x_clk, "pll-audio-2x",
> > > >
> > > >                             clk_parent_pll_audio,
> > > >                             4, 1, CLK_SET_RATE_PARENT);
> > >
> > > You need to fix the factors for the other two outputs as well, since all
> > > three are derived from pll-audio-base.
> >
> > Fix how? pll-audio-2x and pll-audio-4x clocks have fixed divider in regards to
> > pll-audio-base, while pll-audio has not. Unless you mean changing their name?
>
> Argh... I got it wrong. It looks good actually.
>
> Acked-by: Chen-Yu Tsai <wens@...e.org>

Queued for 5.5, thanks

Maxime

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