linux-kernel - [PATCH v2 2/2] clk: aspeed: Prevent reset if clock is enabled

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Date:   Thu,  8 Mar 2018 14:57:20 -0600
From:   Eddie James <eajames@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-clk@...r.kernel.org, joel@....id.au, mturquette@...libre.com,
        sboyd@...nel.org, eajames@...ux.vnet.ibm.com, mine260309@...il.com,
        ryan_chen@...eedtech.com
Subject: [PATCH v2 2/2] clk: aspeed: Prevent reset if clock is enabled

According to the Aspeed specification, the reset and enable sequence
should be done when the clock is stopped. The specification doesn't
define behavior if the reset is done while the clock is enabled.

>From testing on the AST2500, the LPC Controller has problems if the
clock is reset while enabled.

Therefore, check whether the clock is enabled or not before performing
the reset and enable sequence in the Aspeed clock driver.

Root-caused-by: Lei Yu <mine260309@...il.com>
Signed-off-by: Eddie James <eajames@...ux.vnet.ibm.com>
---
 drivers/clk/clk-aspeed.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/drivers/clk/clk-aspeed.c b/drivers/clk/clk-aspeed.c
index 1687771..5eb50c3 100644
--- a/drivers/clk/clk-aspeed.c
+++ b/drivers/clk/clk-aspeed.c
@@ -205,6 +205,18 @@ struct aspeed_clk_soc_data {
 	.calc_pll = aspeed_ast2400_calc_pll,
 };
 
+static int aspeed_clk_is_enabled(struct clk_hw *hw)
+{
+	struct aspeed_clk_gate *gate = to_aspeed_clk_gate(hw);
+	u32 clk = BIT(gate->clock_idx);
+	u32 enval = (gate->flags & CLK_GATE_SET_TO_DISABLE) ? 0 : clk;
+	u32 reg;
+
+	regmap_read(gate->map, ASPEED_CLK_STOP_CTRL, &reg);
+
+	return ((reg & clk) == enval) ? 1 : 0;
+}
+
 static int aspeed_clk_enable(struct clk_hw *hw)
 {
 	struct aspeed_clk_gate *gate = to_aspeed_clk_gate(hw);
@@ -215,6 +227,11 @@ static int aspeed_clk_enable(struct clk_hw *hw)
 
 	spin_lock_irqsave(gate->lock, flags);
 
+	if (aspeed_clk_is_enabled(hw)) {
+		spin_unlock_irqrestore(gate->lock, flags);
+		return 0;
+	}
+
 	if (gate->reset_idx >= 0) {
 		/* Put IP in reset */
 		regmap_update_bits(gate->map, ASPEED_RESET_CTRL, rst, rst);
@@ -255,18 +272,6 @@ static void aspeed_clk_disable(struct clk_hw *hw)
 	spin_unlock_irqrestore(gate->lock, flags);
 }
 
-static int aspeed_clk_is_enabled(struct clk_hw *hw)
-{
-	struct aspeed_clk_gate *gate = to_aspeed_clk_gate(hw);
-	u32 clk = BIT(gate->clock_idx);
-	u32 enval = (gate->flags & CLK_GATE_SET_TO_DISABLE) ? 0 : clk;
-	u32 reg;
-
-	regmap_read(gate->map, ASPEED_CLK_STOP_CTRL, &reg);
-
-	return ((reg & clk) == enval) ? 1 : 0;
-}
-
 static const struct clk_ops aspeed_clk_gate_ops = {
 	.enable = aspeed_clk_enable,
 	.disable = aspeed_clk_disable,
-- 
1.8.3.1