linux-kernel - [PATCH 4.9 13/26] pwm: mxs: Dont modify HW state in .probe() after the PWM chip was registered

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Date:   Fri, 24 Sep 2021 14:44:01 +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, Sascha Hauer <s.hauer@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Thierry Reding <thierry.reding@...il.com>
Subject: [PATCH 4.9 13/26] pwm: mxs: Dont modify HW state in .probe() after the PWM chip was registered

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

commit 020162d6f49f2963062229814a56a89c86cbeaa8 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 reset before calling pwmchip_add().

Note that reseting the hardware isn't the right thing to do if the PWM
is already running as it might e.g. disable (or even enable) a backlight
that is supposed to be on (or off).

Fixes: 4dce82c1e840 ("pwm: add pwm-mxs support")
Cc: Sascha Hauer <s.hauer@...gutronix.de>
Cc: Shawn Guo <shawnguo@...nel.org>
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-mxs.c |   13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

--- a/drivers/pwm/pwm-mxs.c
+++ b/drivers/pwm/pwm-mxs.c
@@ -158,6 +158,11 @@ static int mxs_pwm_probe(struct platform
 		return ret;
 	}
 
+	/* FIXME: Only do this if the PWM isn't already running */
+	ret = stmp_reset_block(mxs->base);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret, "failed to reset PWM\n");
+
 	ret = pwmchip_add(&mxs->chip);
 	if (ret < 0) {
 		dev_err(&pdev->dev, "failed to add pwm chip %d\n", ret);
@@ -166,15 +171,7 @@ static int mxs_pwm_probe(struct platform
 
 	platform_set_drvdata(pdev, mxs);
 
-	ret = stmp_reset_block(mxs->base);
-	if (ret)
-		goto pwm_remove;
-
 	return 0;
-
-pwm_remove:
-	pwmchip_remove(&mxs->chip);
-	return ret;
 }
 
 static int mxs_pwm_remove(struct platform_device *pdev)