linux-kernel - [PATCH 1/2] clk: ingenic: Fix round_rate misbehaving with non-integer dividers

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Message-Id: <20190128020921.16309-1-paul@crapouillou.net>
Date:   Sun, 27 Jan 2019 23:09:20 -0300
From:   Paul Cercueil <paul@...pouillou.net>
To:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     Maarten ter Huurne <maarten@...ewalker.org>,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paul Cercueil <paul@...pouillou.net>, stable@...r.kernel.org
Subject: [PATCH 1/2] clk: ingenic: Fix round_rate misbehaving with non-integer dividers

Take a parent rate of 180 MHz, and a requested rate of 4.285715 MHz.
This results in a theorical divider of 41.999993 which is then rounded
up to 42. The .round_rate function would then return (180 MHz / 42) as
the clock, rounded down, so 4.285714 MHz.

Calling clk_set_rate on 4.285714 MHz would round the rate again, and
give a theorical divider of 42,0000028, now rounded up to 43, and the
rate returned would be (180 MHz / 43) which is 4.186046 MHz, aka. not
what we requested.

Fix this by rounding up the divisions.

Signed-off-by: Paul Cercueil <paul@...pouillou.net>
Tested-by: Maarten ter Huurne <maarten@...ewalker.org>
Cc: <stable@...r.kernel.org>
---
 drivers/clk/ingenic/cgu.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/clk/ingenic/cgu.c b/drivers/clk/ingenic/cgu.c
index 5ef7d9ba2195..b40160eb3372 100644
--- a/drivers/clk/ingenic/cgu.c
+++ b/drivers/clk/ingenic/cgu.c
@@ -426,16 +426,16 @@ ingenic_clk_round_rate(struct clk_hw *hw, unsigned long req_rate,
 	struct ingenic_clk *ingenic_clk = to_ingenic_clk(hw);
 	struct ingenic_cgu *cgu = ingenic_clk->cgu;
 	const struct ingenic_cgu_clk_info *clk_info;
-	long rate = *parent_rate;
+	unsigned int div = 1;
 
 	clk_info = &cgu->clock_info[ingenic_clk->idx];
 
 	if (clk_info->type & CGU_CLK_DIV)
-		rate /= ingenic_clk_calc_div(clk_info, *parent_rate, req_rate);
+		div = ingenic_clk_calc_div(clk_info, *parent_rate, req_rate);
 	else if (clk_info->type & CGU_CLK_FIXDIV)
-		rate /= clk_info->fixdiv.div;
+		div = clk_info->fixdiv.div;
 
-	return rate;
+	return DIV_ROUND_UP(*parent_rate, div);
 }
 
 static int
@@ -455,7 +455,7 @@ ingenic_clk_set_rate(struct clk_hw *hw, unsigned long req_rate,
 
 	if (clk_info->type & CGU_CLK_DIV) {
 		div = ingenic_clk_calc_div(clk_info, parent_rate, req_rate);
-		rate = parent_rate / div;
+		rate = DIV_ROUND_UP(parent_rate, div);
 
 		if (rate != req_rate)
 			return -EINVAL;
-- 
2.20.1.495.gaa96b0ce6b