linux-kernel - [PATCH 3.16 026/114] pinctrl: single: Fix pcs_parse_bits_in_pinctrl_entry to use _

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Message-ID: <lsq.1465842997.977280513@decadent.org.uk>
Date:	Mon, 13 Jun 2016 19:36:37 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Linus Walleij" <linus.walleij@...aro.org>,
	"Tony Lindgren" <tony@...mide.com>, "Keerthy" <j-keerthy@...com>
Subject: [PATCH 3.16 026/114] pinctrl: single: Fix pcs_parse_bits_in_pinctrl_entry
 to use __ffs than ffs

3.16.36-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Keerthy <j-keerthy@...com>

commit 56b367c0cd67d4c3006738e7dc9dda9273fd2bfe upstream.

pcs_parse_bits_in_pinctrl_entry uses ffs which gives bit indices
ranging from 1 to MAX. This leads to a corner case where we try to request
the pin number = MAX and fails.

bit_pos value is being calculted using ffs. pin_num_from_lsb uses
bit_pos value. pins array is populated with:

pin + pin_num_from_lsb.

The above is 1 more than usual bit indices as bit_pos uses ffs to compute
first set bit. Hence the last of the pins array is populated with the MAX
value and not MAX - 1 which causes error when we call pin_request.

mask_pos is rightly calculated as ((pcs->fmask) << (bit_pos - 1))
Consequently val_pos and submask are correct.

Hence use __ffs which gives (ffs(x) - 1) as the first bit set.

fixes: 4e7e8017a8 ("pinctrl: pinctrl-single: enhance to configure multiple pins of different modules")
Signed-off-by: Keerthy <j-keerthy@...com>
Acked-by: Tony Lindgren <tony@...mide.com>
Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/pinctrl/pinctrl-single.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/pinctrl/pinctrl-single.c
+++ b/drivers/pinctrl/pinctrl-single.c
@@ -1329,9 +1329,9 @@ static int pcs_parse_bits_in_pinctrl_ent
 
 		/* Parse pins in each row from LSB */
 		while (mask) {
-			bit_pos = ffs(mask);
+			bit_pos = __ffs(mask);
 			pin_num_from_lsb = bit_pos / pcs->bits_per_pin;
-			mask_pos = ((pcs->fmask) << (bit_pos - 1));
+			mask_pos = ((pcs->fmask) << bit_pos);
 			val_pos = val & mask_pos;
 			submask = mask & mask_pos;
 
@@ -1908,7 +1908,7 @@ static int pcs_probe(struct platform_dev
 	ret = of_property_read_u32(np, "pinctrl-single,function-mask",
 				   &pcs->fmask);
 	if (!ret) {
-		pcs->fshift = ffs(pcs->fmask) - 1;
+		pcs->fshift = __ffs(pcs->fmask);
 		pcs->fmax = pcs->fmask >> pcs->fshift;
 	} else {
 		/* If mask property doesn't exist, function mux is invalid. */