linux-kernel - [PATCH] pwm: Fix period and polarity in pwm

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Date:	Wed, 13 Aug 2014 17:18:53 +0200
From:	Geert Uytterhoeven <geert+renesas@...der.be>
To:	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:	Haavard Skinnemoen <hskinnemoen@...il.com>,
	Hans-Christian Egtvedt <egtvedt@...fundet.no>,
	linux-pwm@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	stable@...r.kernel.org
Subject: [PATCH] pwm: Fix period and polarity in pwm_get() for non-perfect matches

If pwm_get() finds a look-up entry with a perfect match (both dev_id and
con_id match), the loop is aborted, and "p" still points to the correct
struct pwm_lookup.

If only an entry with a matching dev_id or con_id is found, the loop
terminates after traversing the whole list, and "p" now points to
arbitrary memory, not part of the pwm_lookup list.
Then pwm_set_period() and pwm_set_polarity() will set random values for
period resp. polarity.

To fix this, save period and polarity when finding a new best match,
just like is done for chip (for the provider) and index.

This fixes the LCD backlight on r8a7740/armadillo-legacy, which was fed
period 0 and polarity -1068821144 instead of 33333 resp. 1.

Fixes: 3796ce1d4d4b330a75005c5eda105603ce9d4071 ("pwm: add period and polarity to struct pwm_lookup")
Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
Cc: stable@...r.kernel.org
---
 drivers/pwm/core.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index 4b66bf09ee55..d2c35920ff08 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -606,6 +606,8 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
 	unsigned int best = 0;
 	struct pwm_lookup *p;
 	unsigned int match;
+	unsigned int period;
+	enum pwm_polarity polarity;
 
 	/* look up via DT first */
 	if (IS_ENABLED(CONFIG_OF) && dev && dev->of_node)
@@ -653,6 +655,8 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
 		if (match > best) {
 			chip = pwmchip_find_by_name(p->provider);
 			index = p->index;
+			period = p->period;
+			polarity = p->polarity;
 
 			if (match != 3)
 				best = match;
@@ -668,8 +672,8 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
 	if (IS_ERR(pwm))
 		return pwm;
 
-	pwm_set_period(pwm, p->period);
-	pwm_set_polarity(pwm, p->polarity);
+	pwm_set_period(pwm, period);
+	pwm_set_polarity(pwm, polarity);
 
 
 	return pwm;
-- 
1.9.1

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