From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rob Herring Subject: [PATCH 4/7] clk: highbank: prevent glitching when going into bypass mode Date: Wed, 4 Dec 2013 17:35:24 -0600 Message-ID: <1386200127-23143-5-git-send-email-robherring2@gmail.com> References: <1386200127-23143-1-git-send-email-robherring2@gmail.com> Return-path: In-Reply-To: <1386200127-23143-1-git-send-email-robherring2@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: linux-kernel@vger.kernel.org, devicetree@vger.kernel.org Cc: Mike Turquette , Mark Langsdorf , Rob Herring List-Id: devicetree@vger.kernel.org From: Mark Langsdorf Under very rare circumstances, the clock multiplexer can take around 100 ns to enter bypass mode. Attempting to reprogram the clock PLL before the clock has fully entered bypass mode can cause errors in the system, up to and including kernel panics. Add a 300 ns delay after programming the bypass enable to make sure that bypass mode has been enabled. This patch should be added to the stable series. Signed-off-by: Mark Langsdorf Cc: Mike Turquette Signed-off-by: Rob Herring --- drivers/clk/clk-highbank.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/clk/clk-highbank.c b/drivers/clk/clk-highbank.c index 2e7e9d9..dc7ca30 100644 --- a/drivers/clk/clk-highbank.c +++ b/drivers/clk/clk-highbank.c @@ -21,6 +21,7 @@ #include #include #include +#include #define HB_PLL_LOCK_500 0x20000000 #define HB_PLL_LOCK 0x10000000 @@ -167,6 +168,8 @@ static int clk_pll_set_rate(struct clk_hw *hwclk, unsigned long rate, /* Need to re-lock PLL, so put it into bypass mode */ reg |= HB_PLL_EXT_BYPASS; writel(reg | HB_PLL_EXT_BYPASS, hbclk->reg); + /* delay to make sure we are in bypass */ + ndelay(300); writel(reg | HB_PLL_RESET, hbclk->reg); reg &= ~(HB_PLL_DIVF_MASK | HB_PLL_DIVQ_MASK); @@ -182,6 +185,9 @@ static int clk_pll_set_rate(struct clk_hw *hwclk, unsigned long rate, reg &= ~HB_PLL_EXT_BYPASS; } else { writel(reg | HB_PLL_EXT_BYPASS, hbclk->reg); + /* delay to make sure we are in bypass */ + ndelay(300); + reg &= ~HB_PLL_DIVQ_MASK; reg |= divq << HB_PLL_DIVQ_SHIFT; writel(reg | HB_PLL_EXT_BYPASS, hbclk->reg); -- 1.8.3.2