From: Jernej Skrabec <jernej.skrabec@siol.net>
To: maxime.ripard@bootlin.com, wens@csie.org
Cc: jernej.skrabec@siol.net, sboyd@kernel.org,
mturquette@baylibre.com, linux-kernel@vger.kernel.org,
linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2 2/2] clk: sunxi-ng: nkmp: Explain why zero width check is needed
Date: Wed, 3 Apr 2019 17:14:04 +0200 [thread overview]
Message-ID: <20190403151404.26542-3-jernej.skrabec@siol.net> (raw)
In-Reply-To: <20190403151404.26542-1-jernej.skrabec@siol.net>
Add an explanation why zero width check is needed when generating factor
mask using GENMASK() macro.
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
---
drivers/clk/sunxi-ng/ccu_nkmp.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/clk/sunxi-ng/ccu_nkmp.c b/drivers/clk/sunxi-ng/ccu_nkmp.c
index 69dfc6de1c4e..cbcdf664f336 100644
--- a/drivers/clk/sunxi-ng/ccu_nkmp.c
+++ b/drivers/clk/sunxi-ng/ccu_nkmp.c
@@ -186,6 +186,12 @@ static int ccu_nkmp_set_rate(struct clk_hw *hw, unsigned long rate,
ccu_nkmp_find_best(parent_rate, rate, &_nkmp);
+ /*
+ * If width is 0, GENMASK() macro may not generate expected mask (0)
+ * as it falls under undefined behaviour by C standard due to shifts
+ * which are equal or greater than width of left operand. This can
+ * be easily avoided by explicitly checking if width is 0.
+ */
if (nkmp->n.width)
n_mask = GENMASK(nkmp->n.width + nkmp->n.shift - 1,
nkmp->n.shift);
--
2.21.0
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next prev parent reply other threads:[~2019-04-03 15:14 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-03 15:14 [PATCH v2 0/2] clk: sunxi-ng: H6 related clock fixes Jernej Skrabec
2019-04-03 15:14 ` [PATCH v2 1/2] clk: sunxi-ng: h6: Allow video & vpu clocks to change parent rate Jernej Skrabec
2019-04-03 15:14 ` Jernej Skrabec [this message]
2019-04-04 7:32 ` [PATCH v2 0/2] clk: sunxi-ng: H6 related clock fixes Maxime Ripard
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