[PATCH] clk: imx: gate off peripheral clock slice

[Peng Fan (OSS)]

From: Peng Fan <peng.fan at nxp.com>

The Peripheral clocks are default enabled when SoC power on, and
bootloader not gate off the clocks when booting Linux Kernel.

So Linux Kernel is not aware the peripheral clocks are enabled and
still take them as disabled because of enable count is zero.

Then Peripheral clock's source without clock gated off could be
changed when have assigned-parents in device tree

However, per i.MX8M* reference mannual, "Peripheral clock slices must
be stopped to change the clock source", so need to gate off the
the peripheral clock when registering the clocks to avoid glitch.

Tested boot on i.MX8MM/P-EVK board

Signed-off-by: Peng Fan <peng.fan at nxp.com>
---
 drivers/clk/imx/clk-composite-8m.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/imx/clk-composite-8m.c b/drivers/clk/imx/clk-composite-8m.c
index 2dfd6149e528..ee41fbf90589 100644
--- a/drivers/clk/imx/clk-composite-8m.c
+++ b/drivers/clk/imx/clk-composite-8m.c
@@ -184,6 +184,7 @@ struct clk_hw *__imx8m_clk_hw_composite(const char *name,
 	struct clk_mux *mux = NULL;
 	const struct clk_ops *divider_ops;
 	const struct clk_ops *mux_ops;
+	u32 val;
 
 	mux = kzalloc(sizeof(*mux), GFP_KERNEL);
 	if (!mux)
@@ -216,8 +217,14 @@ struct clk_hw *__imx8m_clk_hw_composite(const char *name,
 		div->width = PCG_PREDIV_WIDTH;
 		divider_ops = &imx8m_clk_composite_divider_ops;
 		mux_ops = &clk_mux_ops;
-		if (!(composite_flags & IMX_COMPOSITE_FW_MANAGED))
+		if (!(composite_flags & IMX_COMPOSITE_FW_MANAGED)) {
 			flags |= CLK_SET_PARENT_GATE;
+			if (!(flags & CLK_IS_CRITICAL)) {
+				val = readl(reg);
+				val &= ~BIT(PCG_CGC_SHIFT);
+				writel(val, reg);
+			}
+		}
 	}
 
 	div->lock = &imx_ccm_lock;
-- 
2.30.0