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

On Wed, Sep 18, 2019 at 1:21 PM Jernej Škrabec [off-list ref] wrote:

Dne torek, 17. september 2019 ob 08:54:08 CEST je Chen-Yu Tsai napisal(a):

quoted

On Sat, Sep 14, 2019 at 9:51 PM Jernej Skrabec [off-list ref]

wrote:

quoted

quoted

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 <redacted>
---

 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 <redacted>

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