linux-kernel - [PATCH] clk: imx: Fix fractional clock set rate computation

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Message-ID: <1547816041-14200-1-git-send-email-abel.vesa@nxp.com>
Date:   Fri, 18 Jan 2019 12:54:13 +0000
From:   Abel Vesa <abel.vesa@....com>
To:     Stephen Boyd <sboyd@...nel.org>,
        Lucas Stach <l.stach@...gutronix.de>
CC:     Abel Vesa <abel.vesa@....com>, Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        dl-linux-imx <linux-imx@....com>,
        Michael Turquette <mturquette@...libre.com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:COMMON CLK FRAMEWORK" <linux-clk@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: [PATCH] clk: imx: Fix fractional clock set rate computation

Before multiplying by PLL_FRAC_DENOM, the temp64 needs to be
 temp64 = rate * 2 - divfi * parent_rate * 8, instead of:
 temp64 = (rate * 2 - divfi) * parent_rate

Fixes: 6209624b9a5c1e ("clk: imx: Add fractional PLL output clock")
Signed-off-by: Abel Vesa <abel.vesa@....com>
---
 drivers/clk/imx/clk-frac-pll.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/imx/clk-frac-pll.c b/drivers/clk/imx/clk-frac-pll.c
index 0026c39..76b9eb1 100644
--- a/drivers/clk/imx/clk-frac-pll.c
+++ b/drivers/clk/imx/clk-frac-pll.c
@@ -155,13 +155,14 @@ static int clk_pll_set_rate(struct clk_hw *hw, unsigned long rate,
 {
 	struct clk_frac_pll *pll = to_clk_frac_pll(hw);
 	u32 val, divfi, divff;
-	u64 temp64 = parent_rate;
+	u64 temp64;
 	int ret;
 
 	parent_rate *= 8;
 	rate *= 2;
 	divfi = rate / parent_rate;
-	temp64 *= rate - divfi;
+	temp64 = parent_rate * divfi;
+	temp64 = rate - temp64;
 	temp64 *= PLL_FRAC_DENOM;
 	do_div(temp64, parent_rate);
 	divff = temp64;
-- 
2.7.4