[PATCH 4.4 09/23] pwm: mxs: Dont modify HW state in .probe() after the PWM chip was registered

Greg Kroah-Hartman
2021-09-24T12:45:52Z

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
@@ -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)