clk: sunxi-ng: sun6i: Use sigma-delta modulation for audio PLL

The audio blocks require specific clock rates. Until now we were using
the closest clock rate possible with integer N-M factors. This resulted
in audio playback being slightly slower than it should be.

The vendor kernel gets around this (for newer SoCs) by using sigma-delta
modulation to generate a fractional-N factor. As the PLL hardware is
identical in most chips, we can back port the settings from the newer
SoC, in this case the H3, onto the A31.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

diff --git a/drivers/clk/sunxi-ng/ccu-sun6i-a31.c b/drivers/clk/sunxi-ng/ccu-sun6i-a31.c
index 241fb13..72b16ed 100644 (file)
--- a/drivers/clk/sunxi-ng/ccu-sun6i-a31.c
+++ b/drivers/clk/sunxi-ng/ccu-sun6i-a31.c
@@ -31,6 +31,7 @@
 #include "ccu_nkmp.h"
 #include "ccu_nm.h"
 #include "ccu_phase.h"
+#include "ccu_sdm.h"
 
 #include "ccu-sun6i-a31.h"
 
@@ -48,18 +49,29 @@ static SUNXI_CCU_NKM_WITH_GATE_LOCK(pll_cpu_clk, "pll-cpu",
  * the base (2x, 4x and 8x), and one variable divider (the one true
  * pll audio).
  *
- * We don't have any need for the variable divider for now, so we just
- * hardcode it to match with the clock names
+ * With sigma-delta modulation for fractional-N on the audio PLL,
+ * we have to use specific dividers. This means the variable divider
+ * can no longer be used, as the audio codec requests the exact clock
+ * rates we support through this mechanism. So we now hard code the
+ * variable divider to 1. This means the clock rates will no longer
+ * match the clock names.
  */
 #define SUN6I_A31_PLL_AUDIO_REG        0x008
 
-static SUNXI_CCU_NM_WITH_GATE_LOCK(pll_audio_base_clk, "pll-audio-base",
-                                  "osc24M", 0x008,
-                                  8, 7,        /* N */
-                                  0, 5,        /* M */
-                                  BIT(31),     /* gate */
-                                  BIT(28),     /* lock */
-                                  CLK_SET_RATE_UNGATE);
+static struct ccu_sdm_setting pll_audio_sdm_table[] = {
+       { .rate = 22579200, .pattern = 0xc0010d84, .m = 8, .n = 7 },
+       { .rate = 24576000, .pattern = 0xc000ac02, .m = 14, .n = 14 },
+};
+
+static SUNXI_CCU_NM_WITH_SDM_GATE_LOCK(pll_audio_base_clk, "pll-audio-base",
+                                      "osc24M", 0x008,
+                                      8, 7,    /* N */
+                                      0, 5,    /* M */
+                                      pll_audio_sdm_table, BIT(24),
+                                      0x284, BIT(31),
+                                      BIT(31), /* gate */
+                                      BIT(28), /* lock */
+                                      CLK_SET_RATE_UNGATE);
 
 static SUNXI_CCU_NM_WITH_FRAC_GATE_LOCK(pll_video0_clk, "pll-video0",
                                        "osc24M", 0x010,
@@ -950,9 +962,9 @@ static struct ccu_common *sun6i_a31_ccu_clks[] = {
        &out_c_clk.common,
 };
 
-/* We hardcode the divider to 4 for now */
+/* We hardcode the divider to 1 for now */
 static CLK_FIXED_FACTOR(pll_audio_clk, "pll-audio",
-                       "pll-audio-base", 4, 1, CLK_SET_RATE_PARENT);
+                       "pll-audio-base", 1, 1, CLK_SET_RATE_PARENT);
 static CLK_FIXED_FACTOR(pll_audio_2x_clk, "pll-audio-2x",
                        "pll-audio-base", 2, 1, CLK_SET_RATE_PARENT);
 static CLK_FIXED_FACTOR(pll_audio_4x_clk, "pll-audio-4x",
@@ -1221,10 +1233,10 @@ static void __init sun6i_a31_ccu_setup(struct device_node *node)
                return;
        }
 
-       /* Force the PLL-Audio-1x divider to 4 */
+       /* Force the PLL-Audio-1x divider to 1 */
        val = readl(reg + SUN6I_A31_PLL_AUDIO_REG);
        val &= ~GENMASK(19, 16);
-       writel(val | (3 << 16), reg + SUN6I_A31_PLL_AUDIO_REG);
+       writel(val | (0 << 16), reg + SUN6I_A31_PLL_AUDIO_REG);
 
        /* Force PLL-MIPI to MIPI mode */
        val = readl(reg + SUN6I_A31_PLL_MIPI_REG);