linux-kernel - [PATCH v3 1/7] clk: meson: add 'NOINIT_ENABLED' flag to eliminate init for enabled PLL

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Date: Wed, 15 May 2024 21:47:24 +0300
From: Dmitry Rokosov <ddrokosov@...utedevices.com>
To: <neil.armstrong@...aro.org>, <jbrunet@...libre.com>,
	<mturquette@...libre.com>, <sboyd@...nel.org>, <robh+dt@...nel.org>,
	<krzysztof.kozlowski+dt@...aro.org>, <khilman@...libre.com>,
	<martin.blumenstingl@...glemail.com>
CC: <jian.hu@...ogic.com>, <kernel@...rdevices.ru>, <rockosov@...il.com>,
	<linux-amlogic@...ts.infradead.org>, <linux-clk@...r.kernel.org>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, Dmitry Rokosov
	<ddrokosov@...utedevices.com>
Subject: [PATCH v3 1/7] clk: meson: add 'NOINIT_ENABLED' flag to eliminate init for enabled PLL

When dealing with certain PLLs, it is necessary to avoid modifying them
if they have already been initialized by lower levels. For instance, in
the A1 SoC Family, the sys_pll is enabled as the parent for the cpuclk,
and it cannot be disabled during the initialization sequence. Therefore,
initialization phase must be skipped.

Signed-off-by: Dmitry Rokosov <ddrokosov@...utedevices.com>
---
 drivers/clk/meson/clk-pll.c | 40 ++++++++++++++++++++++---------------
 drivers/clk/meson/clk-pll.h |  1 +
 2 files changed, 25 insertions(+), 16 deletions(-)

diff --git a/drivers/clk/meson/clk-pll.c b/drivers/clk/meson/clk-pll.c
index 78d17b2415af..e1132a110aab 100644
--- a/drivers/clk/meson/clk-pll.c
+++ b/drivers/clk/meson/clk-pll.c
@@ -289,11 +289,35 @@ static int meson_clk_pll_wait_lock(struct clk_hw *hw)
 	return -ETIMEDOUT;
 }
 
+static int meson_clk_pll_is_enabled(struct clk_hw *hw)
+{
+	struct clk_regmap *clk = to_clk_regmap(hw);
+	struct meson_clk_pll_data *pll = meson_clk_pll_data(clk);
+
+	if (MESON_PARM_APPLICABLE(&pll->rst) &&
+	    meson_parm_read(clk->map, &pll->rst))
+		return 0;
+
+	if (!meson_parm_read(clk->map, &pll->en) ||
+	    !meson_parm_read(clk->map, &pll->l))
+		return 0;
+
+	return 1;
+}
+
 static int meson_clk_pll_init(struct clk_hw *hw)
 {
 	struct clk_regmap *clk = to_clk_regmap(hw);
 	struct meson_clk_pll_data *pll = meson_clk_pll_data(clk);
 
+	/*
+	 * Keep the clock running, which was already initialized and enabled
+	 * from the bootloader stage, to avoid any glitches.
+	 */
+	if ((pll->flags & CLK_MESON_PLL_NOINIT_ENABLED) &&
+	    meson_clk_pll_is_enabled(hw))
+		return 0;
+
 	if (pll->init_count) {
 		if (MESON_PARM_APPLICABLE(&pll->rst))
 			meson_parm_write(clk->map, &pll->rst, 1);
@@ -308,22 +332,6 @@ static int meson_clk_pll_init(struct clk_hw *hw)
 	return 0;
 }
 
-static int meson_clk_pll_is_enabled(struct clk_hw *hw)
-{
-	struct clk_regmap *clk = to_clk_regmap(hw);
-	struct meson_clk_pll_data *pll = meson_clk_pll_data(clk);
-
-	if (MESON_PARM_APPLICABLE(&pll->rst) &&
-	    meson_parm_read(clk->map, &pll->rst))
-		return 0;
-
-	if (!meson_parm_read(clk->map, &pll->en) ||
-	    !meson_parm_read(clk->map, &pll->l))
-		return 0;
-
-	return 1;
-}
-
 static int meson_clk_pcie_pll_enable(struct clk_hw *hw)
 {
 	int retries = 10;
diff --git a/drivers/clk/meson/clk-pll.h b/drivers/clk/meson/clk-pll.h
index a2228c0fdce5..7b6b87274073 100644
--- a/drivers/clk/meson/clk-pll.h
+++ b/drivers/clk/meson/clk-pll.h
@@ -28,6 +28,7 @@ struct pll_mult_range {
 	}
 
 #define CLK_MESON_PLL_ROUND_CLOSEST	BIT(0)
+#define CLK_MESON_PLL_NOINIT_ENABLED	BIT(1)
 
 struct meson_clk_pll_data {
 	struct parm en;
-- 
2.43.0