linux-kernel - [PATCH 2/7] clk: thead: th1520-ap: Poll for PLL lock and wait for stability

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Message-ID: <20251120131416.26236-3-ziyao@disroot.org>
Date: Thu, 20 Nov 2025 13:14:11 +0000
From: Yao Zi <ziyao@...root.org>
To: Drew Fustini <fustini@...nel.org>,
	Guo Ren <guoren@...nel.org>,
	Fu Wei <wefu@...hat.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Paul Walmsley <pjw@...nel.org>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Alexandre Ghiti <alex@...ti.fr>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>,
	Icenowy Zheng <uwu@...nowy.me>
Cc: linux-riscv@...ts.infradead.org,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-clk@...r.kernel.org,
	Han Gao <rabenda.cn@...il.com>,
	Han Gao <gaohan@...as.ac.cn>,
	Yao Zi <ziyao@...root.org>
Subject: [PATCH 2/7] clk: thead: th1520-ap: Poll for PLL lock and wait for stability

All PLLs found on TH1520 SoC take 21250ns at maximum to lock, and their
lock status is indicated by register PLL_STS (offset 0x80 inside AP
clock controller). We should poll the register to ensure the PLL
actually locks after enabling it.

Furthermore, a 30us delay is added after enabling the PLL, after which
the PLL could be considered stable as stated by vendor clock code.

Fixes: 56a48c1833aa ("clk: thead: add support for enabling/disabling PLLs")
Signed-off-by: Yao Zi <ziyao@...root.org>
---
 drivers/clk/thead/clk-th1520-ap.c | 34 +++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/thead/clk-th1520-ap.c b/drivers/clk/thead/clk-th1520-ap.c
index 71ad03a998e8..d870f0c665f8 100644
--- a/drivers/clk/thead/clk-th1520-ap.c
+++ b/drivers/clk/thead/clk-th1520-ap.c
@@ -8,11 +8,14 @@
 #include <dt-bindings/clock/thead,th1520-clk-ap.h>
 #include <linux/bitfield.h>
 #include <linux/clk-provider.h>
+#include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/regmap.h>
 
+#define TH1520_PLL_STS		0x80
+
 #define TH1520_PLL_POSTDIV2	GENMASK(26, 24)
 #define TH1520_PLL_POSTDIV1	GENMASK(22, 20)
 #define TH1520_PLL_FBDIV	GENMASK(19, 8)
@@ -23,6 +26,13 @@
 #define TH1520_PLL_FRAC		GENMASK(23, 0)
 #define TH1520_PLL_FRAC_BITS    24
 
+/*
+ * All PLLs in TH1520 take 21250ns at maximum to lock, let's take its double
+ * for safety.
+ */
+#define TH1520_PLL_LOCK_TIMEOUT_US	44
+#define TH1520_PLL_STABLE_DELAY_US	30
+
 struct ccu_internal {
 	u8	shift;
 	u8	width;
@@ -64,6 +74,7 @@ struct ccu_div {
 
 struct ccu_pll {
 	struct ccu_common	common;
+	u32			lock_sts_mask;
 };
 
 #define TH_CCU_ARG(_shift, _width)					\
@@ -299,9 +310,21 @@ static void ccu_pll_disable(struct clk_hw *hw)
 static int ccu_pll_enable(struct clk_hw *hw)
 {
 	struct ccu_pll *pll = hw_to_ccu_pll(hw);
+	u32 reg;
+	int ret;
 
-	return regmap_clear_bits(pll->common.map, pll->common.cfg1,
-				 TH1520_PLL_VCO_RST);
+	regmap_clear_bits(pll->common.map, pll->common.cfg1,
+			  TH1520_PLL_VCO_RST);
+
+	ret = regmap_read_poll_timeout_atomic(pll->common.map, TH1520_PLL_STS,
+					      reg, reg & pll->lock_sts_mask,
+					      5, TH1520_PLL_LOCK_TIMEOUT_US);
+	if (ret)
+		return ret;
+
+	udelay(TH1520_PLL_STABLE_DELAY_US);
+
+	return 0;
 }
 
 static int ccu_pll_is_enabled(struct clk_hw *hw)
@@ -389,6 +412,7 @@ static struct ccu_pll cpu_pll0_clk = {
 					      &clk_pll_ops,
 					      CLK_IS_CRITICAL),
 	},
+	.lock_sts_mask		= BIT(1),
 };
 
 static struct ccu_pll cpu_pll1_clk = {
@@ -401,6 +425,7 @@ static struct ccu_pll cpu_pll1_clk = {
 					      &clk_pll_ops,
 					      CLK_IS_CRITICAL),
 	},
+	.lock_sts_mask		= BIT(4),
 };
 
 static struct ccu_pll gmac_pll_clk = {
@@ -413,6 +438,7 @@ static struct ccu_pll gmac_pll_clk = {
 					      &clk_pll_ops,
 					      CLK_IS_CRITICAL),
 	},
+	.lock_sts_mask		= BIT(3),
 };
 
 static const struct clk_hw *gmac_pll_clk_parent[] = {
@@ -433,6 +459,7 @@ static struct ccu_pll video_pll_clk = {
 					      &clk_pll_ops,
 					      CLK_IS_CRITICAL),
 	},
+	.lock_sts_mask		= BIT(7),
 };
 
 static const struct clk_hw *video_pll_clk_parent[] = {
@@ -453,6 +480,7 @@ static struct ccu_pll dpu0_pll_clk = {
 					      &clk_pll_ops,
 					      0),
 	},
+	.lock_sts_mask		= BIT(8),
 };
 
 static const struct clk_hw *dpu0_pll_clk_parent[] = {
@@ -469,6 +497,7 @@ static struct ccu_pll dpu1_pll_clk = {
 					      &clk_pll_ops,
 					      0),
 	},
+	.lock_sts_mask		= BIT(9),
 };
 
 static const struct clk_hw *dpu1_pll_clk_parent[] = {
@@ -485,6 +514,7 @@ static struct ccu_pll tee_pll_clk = {
 					      &clk_pll_ops,
 					      CLK_IS_CRITICAL),
 	},
+	.lock_sts_mask		= BIT(10),
 };
 
 static const struct clk_parent_data c910_i0_parents[] = {
-- 
2.51.2