linux-kernel - [PATCH] clk: qcom: clk-rcg2: Fix wrong RCG clock rate for high parent frequencies

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Message-ID: <20230720083304.28881-1-quic_devipriy@quicinc.com>
Date:   Thu, 20 Jul 2023 14:03:04 +0530
From:   Devi Priya <quic_devipriy@...cinc.com>
To:     <andersson@...nel.org>, <agross@...nel.org>,
        <konrad.dybcio@...aro.org>, <mturquette@...libre.com>,
        <sboyd@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-clk@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <quic_saahtoma@...cinc.com>
Subject: [PATCH] clk: qcom: clk-rcg2: Fix wrong RCG clock rate for high parent frequencies

If the parent clock rate is greater than unsigned long max/2 then
integer overflow happens when calculating the clock rate on 32-bit systems.
As RCG2 uses half integer dividers, the clock rate is first being
multiplied by 2 which will overflow the unsigned long max value. So, use
unsigned long long for rate computations to avoid overflow.

Signed-off-by: Devi Priya <quic_devipriy@...cinc.com>
---
 drivers/clk/qcom/clk-rcg2.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
index e22baf3a7112..42d00b134975 100644
--- a/drivers/clk/qcom/clk-rcg2.c
+++ b/drivers/clk/qcom/clk-rcg2.c
@@ -156,18 +156,18 @@ static int clk_rcg2_set_parent(struct clk_hw *hw, u8 index)
  *            hid_div       n
  */
 static unsigned long
-calc_rate(unsigned long rate, u32 m, u32 n, u32 mode, u32 hid_div)
+calc_rate(unsigned long parent_rate, u32 m, u32 n, u32 mode, u32 hid_div)
 {
+	u64 rate = parent_rate;
+
 	if (hid_div) {
 		rate *= 2;
-		rate /= hid_div + 1;
+		do_div(rate, hid_div + 1);
 	}
 
 	if (mode) {
-		u64 tmp = rate;
-		tmp *= m;
-		do_div(tmp, n);
-		rate = tmp;
+		rate *= m;
+		do_div(rate, n);
 	}
 
 	return rate;
-- 
2.17.1