clk: qcom: clk-rcg2: Fix clock rate overflow for high parent frequencies

[ Upstream commit f7b7d30 ]

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.
Hence, replace the common pattern of doing 64-bit multiplication
and then a do_div() call with simpler mult_frac call.

Fixes: bcd61c0 ("clk: qcom: Add support for root clock generators (RCGs)")
Signed-off-by: Devi Priya <quic_devipriy@quicinc.com>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Link: https://lore.kernel.org/r/20230901073640.4973-1-quic_devipriy@quicinc.com
[bjorn: Also drop unnecessary {} around single statements]
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/clk/qcom/clk-rcg2.c

@@ -139,17 +139,11 @@ static int clk_rcg2_set_parent(struct clk_hw *hw, u8 index)
 static unsigned long
 calc_rate(unsigned long rate, u32 m, u32 n, u32 mode, u32 hid_div)
 {
-	if (hid_div) {
-		rate *= 2;
-		rate /= hid_div + 1;
-	}
+	if (hid_div)
+		rate = mult_frac(rate, 2, hid_div + 1);
 
-	if (mode) {
-		u64 tmp = rate;
-		tmp *= m;
-		do_div(tmp, n);
-		rate = tmp;
-	}
+	if (mode)
+		rate = mult_frac(rate, m, n);
 
 	return rate;
 }