linux-kernel - [PATCH v2 1/1] clk: sunxi-ng: v3s: use sigma-delta modulation for audio-pll

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Message-Id: <20210218112001.479018-2-t.schramm@manjaro.org>
Date:   Thu, 18 Feb 2021 12:20:01 +0100
From:   Tobias Schramm <t.schramm@...jaro.org>
To:     Icenowy Zheng <icenowy@...c.io>, Maxime Ripard <maxime@...no.tech>
Cc:     linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Tobias Schramm <t.schramm@...jaro.org>
Subject: [PATCH v2 1/1] clk: sunxi-ng: v3s: use sigma-delta modulation for audio-pll

Previously it was not possible to achieve clock rates of 24.576MHz and
22.5792MHz, which are commonly required core clocks for the i2s
peripheral of v3s based SoCs.

Add support for those clock rates through the audio pll's sigma-delta
modulator.

Signed-off-by: Tobias Schramm <t.schramm@...jaro.org>
---
 drivers/clk/sunxi-ng/ccu-sun8i-v3s.c | 33 ++++++++++++++++++----------
 1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/drivers/clk/sunxi-ng/ccu-sun8i-v3s.c b/drivers/clk/sunxi-ng/ccu-sun8i-v3s.c
index 0e36ca3bf3d5..a774942cb153 100644
--- a/drivers/clk/sunxi-ng/ccu-sun8i-v3s.c
+++ b/drivers/clk/sunxi-ng/ccu-sun8i-v3s.c
@@ -40,18 +40,29 @@ static SUNXI_CCU_NKMP_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 SUN8I_V3S_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 */
-				   0);
+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_video_clk, "pll-video",
 					"osc24M", 0x0010,
@@ -524,10 +535,10 @@ static struct ccu_common *sun8i_v3_ccu_clks[] = {
 	&mipi_csi_clk.common,
 };
 
-/* We hardcode the divider to 4 for now */
+/* We hardcode the divider to 1 for SDM support */
 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);
-- 
2.30.1