[PATCH] BUG: pinmux: forbid mux_usecount to be set at UINT_MAX

[Richard Genoud <richard.genoud@gmail.com>]

If pin_free is called on a pin already freed, mux_usecount is set to
UINT_MAX which is really a bad idea.
This will issue a warning, so that we can correct the code responsible
for the double free.

Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
---
Ok Stephen, your idea (and code) seems better.
I signed-off it, but it's really yours...
Feel free to transform my Signed-off-by in a Tested-by

 drivers/pinctrl/pinmux.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/drivers/pinctrl/pinmux.c b/drivers/pinctrl/pinmux.c
index 1a00658..bd83c8b 100644
--- a/drivers/pinctrl/pinmux.c
+++ b/drivers/pinctrl/pinmux.c
@@ -194,6 +194,11 @@ static const char *pin_free(struct pinctrl_dev *pctldev, int pin,
 	}
 
 	if (!gpio_range) {
+		/*
+		 * A pin should not be freed more times than allocated.
+		 */
+		if (WARN_ON(!desc->mux_usecount))
+			return NULL;
 		desc->mux_usecount--;
 		if (desc->mux_usecount)
 			return NULL;
-- 
1.7.2.5