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clk: sunxi-ng: nkmp: Explain why zero width check is needed 

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>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
This commit is contained in:
Jernej Skrabec 2019-04-03 17:14:04 +02:00 committed by Maxime Ripard
parent 2abc330c51
commit 1054e4dd1c
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1 changed files with 6 additions and 0 deletions
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6
drivers/clk/sunxi-ng/ccu_nkmp.c
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@ -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); 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) if (nkmp->n.width)
n_mask = GENMASK(nkmp->n.width + nkmp->n.shift - 1, n_mask = GENMASK(nkmp->n.width + nkmp->n.shift - 1,
nkmp->n.shift); nkmp->n.shift);