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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Sascha Hauer <s.hauer@pengutronix.de>,
        Shawn Guo <shawnguo@kernel.org>,
        =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>,
        Thierry Reding <thierry.reding@gmail.com>
Subject: [PATCH 4.19 16/34] pwm: mxs: Dont modify HW state in .probe() after the PWM chip was registered
Date:   Fri, 24 Sep 2021 14:44:10 +0200
Message-Id: <20210924124330.492622344@linuxfoundation.org>
In-Reply-To: <20210924124329.965218583@linuxfoundation.org>
References: <20210924124329.965218583@linuxfoundation.org>
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From: Uwe Kleine-König <u.kleine-koenig@pengutronix.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@pengutronix.de>
Cc: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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
@@ -152,6 +152,11 @@ 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);
@@ -160,15 +165,7 @@ 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)