linux-kernel - [PATCH v2 1/4] clk: imx: lpcg-scu: SW workaround for errata (e10858)

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Message-Id: <20241018-imx-clk-v1-v2-1-92c0b66ca970@nxp.com>
Date: Fri, 18 Oct 2024 18:00:55 +0800
From: "Peng Fan (OSS)" <peng.fan@....nxp.com>
To: Abel Vesa <abelvesa@...nel.org>, 
 Michael Turquette <mturquette@...libre.com>, 
 Stephen Boyd <sboyd@...nel.org>, Shawn Guo <shawnguo@...nel.org>, 
 Sascha Hauer <s.hauer@...gutronix.de>, 
 Pengutronix Kernel Team <kernel@...gutronix.de>, 
 Fabio Estevam <festevam@...il.com>, Aisheng Dong <aisheng.dong@....com>
Cc: linux-clk@...r.kernel.org, imx@...ts.linux.dev, 
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Peng Fan <peng.fan@....com>
Subject: [PATCH v2 1/4] clk: imx: lpcg-scu: SW workaround for errata
 (e10858)

From: Peng Fan <peng.fan@....com>

Back-to-back LPCG writes can be ignored by the LPCG register due to
a HW bug. The writes need to be separated by at least 4 cycles of
the gated clock. See https://www.nxp.com.cn/docs/en/errata/IMX8_1N94W.pdf

The workaround is implemented as follows:
1. For clocks running greater than or equal to 24MHz, a read
followed by the write will provide sufficient delay.
2. For clocks running below 24MHz, add a delay of 4 clock cylces
after the write to the LPCG register.

Fixes: 2f77296d3df9 ("clk: imx: add lpcg clock support")
Signed-off-by: Peng Fan <peng.fan@....com>
---
 drivers/clk/imx/clk-lpcg-scu.c | 35 +++++++++++++++++++++++++++++++----
 1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/drivers/clk/imx/clk-lpcg-scu.c b/drivers/clk/imx/clk-lpcg-scu.c
index dd5abd09f3e206a5073767561b517d5b3320b28c..cd42190233662c66f2c354f0a2eee3a2531eeb3a 100644
--- a/drivers/clk/imx/clk-lpcg-scu.c
+++ b/drivers/clk/imx/clk-lpcg-scu.c
@@ -6,10 +6,12 @@
 
 #include <linux/bits.h>
 #include <linux/clk-provider.h>
+#include <linux/delay.h>
 #include <linux/err.h>
 #include <linux/io.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
+#include <linux/units.h>
 
 #include "clk-scu.h"
 
@@ -41,6 +43,31 @@ struct clk_lpcg_scu {
 
 #define to_clk_lpcg_scu(_hw) container_of(_hw, struct clk_lpcg_scu, hw)
 
+/* e10858 -LPCG clock gating register synchronization errata */
+static void lpcg_e10858_writel(unsigned long rate, void __iomem *reg, u32 val)
+{
+	u32 reg1;
+
+	writel(val, reg);
+
+	if (rate >= 24 * HZ_PER_MHZ || rate == 0) {
+		/*
+		 * The time taken to access the LPCG registers from the AP core
+		 * through the interconnect is longer than the minimum delay
+		 * of 4 clock cycles required by the errata.
+		 * Adding a readl will provide sufficient delay to prevent
+		 * back-to-back writes.
+		 */
+		reg1 = readl(reg);
+	} else {
+		/*
+		 * For clocks running below 24MHz, wait a minimum of
+		 * 4 clock cycles.
+		 */
+		ndelay(4 * (DIV_ROUND_UP(1000 * HZ_PER_MHZ, rate)));
+	}
+}
+
 static int clk_lpcg_scu_enable(struct clk_hw *hw)
 {
 	struct clk_lpcg_scu *clk = to_clk_lpcg_scu(hw);
@@ -57,7 +84,8 @@ static int clk_lpcg_scu_enable(struct clk_hw *hw)
 		val |= CLK_GATE_SCU_LPCG_HW_SEL;
 
 	reg |= val << clk->bit_idx;
-	writel(reg, clk->reg);
+
+	lpcg_e10858_writel(clk_hw_get_rate(hw), clk->reg, reg);
 
 	spin_unlock_irqrestore(&imx_lpcg_scu_lock, flags);
 
@@ -74,7 +102,7 @@ static void clk_lpcg_scu_disable(struct clk_hw *hw)
 
 	reg = readl_relaxed(clk->reg);
 	reg &= ~(CLK_GATE_SCU_LPCG_MASK << clk->bit_idx);
-	writel(reg, clk->reg);
+	lpcg_e10858_writel(clk_hw_get_rate(hw), clk->reg, reg);
 
 	spin_unlock_irqrestore(&imx_lpcg_scu_lock, flags);
 }
@@ -149,9 +177,8 @@ static int __maybe_unused imx_clk_lpcg_scu_resume(struct device *dev)
 	 * FIXME: Sometimes writes don't work unless the CPU issues
 	 * them twice
 	 */
-
-	writel(clk->state, clk->reg);
 	writel(clk->state, clk->reg);
+	lpcg_e10858_writel(0, clk->reg, clk->state);
 	dev_dbg(dev, "restore lpcg state 0x%x\n", clk->state);
 
 	return 0;

-- 
2.37.1