linux-kernel - [PATCH 4.14 12/27] pwm: lpc32xx: Dont modify HW state in .probe() after the PWM chip was registered

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Message-Id: <20210924124329.583402422@linuxfoundation.org>
Date:   Fri, 24 Sep 2021 14:44:06 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sylvain Lemieux <slemieux@...oint.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Thierry Reding <thierry.reding@...il.com>
Subject: [PATCH 4.14 12/27] pwm: lpc32xx: Dont modify HW state in .probe() after the PWM chip was registered

From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>

commit 3d2813fb17e5fd0d73c1d1442ca0192bde4af10e upstream.

This fixes a race condition: After pwmchip_add() is called there might
already be a consumer and then modifying the hardware behind the
consumer's back is bad. So set the default before.

(Side-note: I don't know what this register setting actually does, if
this modifies the polarity there is an inconsistency because the
inversed polarity isn't considered if the PWM is already running during
.probe().)

Fixes: acfd92fdfb93 ("pwm: lpc32xx: Set PWM_PIN_LEVEL bit to default value")
Cc: Sylvain Lemieux <slemieux@...oint.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/pwm/pwm-lpc32xx.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

--- a/drivers/pwm/pwm-lpc32xx.c
+++ b/drivers/pwm/pwm-lpc32xx.c
@@ -124,17 +124,17 @@ static int lpc32xx_pwm_probe(struct plat
 	lpc32xx->chip.npwm = 1;
 	lpc32xx->chip.base = -1;
 
+	/* If PWM is disabled, configure the output to the default value */
+	val = readl(lpc32xx->base + (lpc32xx->chip.pwms[0].hwpwm << 2));
+	val &= ~PWM_PIN_LEVEL;
+	writel(val, lpc32xx->base + (lpc32xx->chip.pwms[0].hwpwm << 2));
+
 	ret = pwmchip_add(&lpc32xx->chip);
 	if (ret < 0) {
 		dev_err(&pdev->dev, "failed to add PWM chip, error %d\n", ret);
 		return ret;
 	}
 
-	/* When PWM is disable, configure the output to the default value */
-	val = readl(lpc32xx->base + (lpc32xx->chip.pwms[0].hwpwm << 2));
-	val &= ~PWM_PIN_LEVEL;
-	writel(val, lpc32xx->base + (lpc32xx->chip.pwms[0].hwpwm << 2));
-
 	platform_set_drvdata(pdev, lpc32xx);
 
 	return 0;