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

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Date:   Tue, 17 Sep 2019 14:54:08 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Jernej Skrabec <jernej.skrabec@...l.net>
Cc:     Maxime Ripard <mripard@...nel.org>,
        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 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.

ChenYu

> @@ -1215,12 +1224,12 @@ static int sun50i_h6_ccu_probe(struct platform_device *pdev)
>         }
>
>         /*
> -        * Force the post-divider of pll-audio to 8 and the output divider
> -        * of it to 1, to make the clock name represents the real frequency.
> +        * Force the post-divider of pll-audio to 12 and the output divider
> +        * of it to 2, so 24576000 and 22579200 rates can be set exactly.
>          */
>         val = readl(reg + SUN50I_H6_PLL_AUDIO_REG);
>         val &= ~(GENMASK(21, 16) | BIT(0));
> -       writel(val | (7 << 16), reg + SUN50I_H6_PLL_AUDIO_REG);
> +       writel(val | (11 << 16) | BIT(0), reg + SUN50I_H6_PLL_AUDIO_REG);
>
>         /*
>          * First clock parent (osc32K) is unusable for CEC. But since there
> --
> 2.23.0
>
> --
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