linux-kernel - [PATCH] clk: sunxi-ng: sun8i: r40: Use sigma delta modulation for audio PLL

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Message-Id: <20200825131049.1277596-1-jernej.skrabec@siol.net>
Date:   Tue, 25 Aug 2020 15:10:49 +0200
From:   Jernej Skrabec <jernej.skrabec@...l.net>
To:     mripard@...nel.org, wens@...e.org
Cc:     mturquette@...libre.com, sboyd@...nel.org,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: [PATCH] clk: sunxi-ng: sun8i: r40: Use sigma delta modulation for audio PLL

Audio cores need specific clock rates which can't be simply obtained by
adjusting integer multipliers and dividers. HW for such cases supports
delta-sigma modulation which enables fractional multipliers.

Port H3 delta-sigma table to R40. They have identical audio PLLs.

Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
---
 drivers/clk/sunxi-ng/ccu-sun8i-r40.c | 37 ++++++++++++++++++----------
 1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/drivers/clk/sunxi-ng/ccu-sun8i-r40.c b/drivers/clk/sunxi-ng/ccu-sun8i-r40.c
index 23bfe1d12f21..84153418453f 100644
--- a/drivers/clk/sunxi-ng/ccu-sun8i-r40.c
+++ b/drivers/clk/sunxi-ng/ccu-sun8i-r40.c
@@ -45,18 +45,29 @@ static struct ccu_nkmp pll_cpu_clk = {
  * 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 SUN8I_R40_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_MIN_MAX(pll_video0_clk, "pll-video0",
 						"osc24M", 0x0010,
@@ -952,10 +963,10 @@ static const struct clk_hw *clk_parent_pll_audio[] = {
 	&pll_audio_base_clk.common.hw
 };
 
-/* We hardcode the divider to 4 for now */
+/* We hardcode the divider to 1 for now */
 static CLK_FIXED_FACTOR_HWS(pll_audio_clk, "pll-audio",
 			    clk_parent_pll_audio,
-			    4, 1, CLK_SET_RATE_PARENT);
+			    1, 1, CLK_SET_RATE_PARENT);
 static CLK_FIXED_FACTOR_HWS(pll_audio_2x_clk, "pll-audio-2x",
 			    clk_parent_pll_audio,
 			    2, 1, CLK_SET_RATE_PARENT);
@@ -1307,10 +1318,10 @@ static int sun8i_r40_ccu_probe(struct platform_device *pdev)
 	if (IS_ERR(reg))
 		return PTR_ERR(reg);
 
-	/* Force the PLL-Audio-1x divider to 4 */
+	/* Force the PLL-Audio-1x divider to 1 */
 	val = readl(reg + SUN8I_R40_PLL_AUDIO_REG);
 	val &= ~GENMASK(19, 16);
-	writel(val | (3 << 16), reg + SUN8I_R40_PLL_AUDIO_REG);
+	writel(val | (0 << 16), reg + SUN8I_R40_PLL_AUDIO_REG);
 
 	/* Force PLL-MIPI to MIPI mode */
 	val = readl(reg + SUN8I_R40_PLL_MIPI_REG);
-- 
2.28.0