[PATCH] pwm: sl28cpld: fix getting driver data in pwm callbacks

* [PATCH] pwm: sl28cpld: fix getting driver data in pwm callbacks
@ 2020-11-24 21:24 Uwe Kleine-König
  2020-11-24 22:22 ` Michael Walle
  2020-11-30  8:17 ` Michael Walle
  0 siblings, 2 replies; 5+ messages in thread
From: Uwe Kleine-König @ 2020-11-24 21:24 UTC (permalink / raw)
  To: Lee Jones, Michael Walle, Thierry Reding; +Cc: linux-pwm, kernel

Currently .get_state() and .apply() use dev_get_drvdata() on the struct
device related to the pwm chip. This only works after .probe() called
platform_set_drvdata() which in this driver happens only after
pwmchip_add() and so comes possibly too late.

Instead of setting the driver data earlier use the traditional
container_of approach as this way the driver data is conceptually and
computational nearer.

Fixes: 9db33d221efc ("pwm: Add support for sl28cpld PWM controller")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
---
Hello,

in v4 of the driver Michael still used container_of and then changed to
use dev_get_drvdata() as Lee suggested. I didn't notice this suggestion,
otherwise I would have expressed my variance about this already earlier.

I noticed this problem because Michael contacted me via irc and showed
me the resulting oops, so I think applying this before 5.10 would be
good. It's not entirely clear to me why .get_state() is called that
early in his case, but the theory is clear: The callbacks can be called
as soon as pwmchip_add() is called.

Best regards
Uwe

 drivers/pwm/pwm-sl28cpld.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/pwm/pwm-sl28cpld.c b/drivers/pwm/pwm-sl28cpld.c
index 5046b6b7fd35..b4c651fc749c 100644
--- a/drivers/pwm/pwm-sl28cpld.c
+++ b/drivers/pwm/pwm-sl28cpld.c
@@ -84,12 +84,14 @@ struct sl28cpld_pwm {
 	struct regmap *regmap;
 	u32 offset;
 };
+#define sl28cpld_pwm_from_chip(_chip) \
+	container_of(_chip, struct sl28cpld_pwm, pwm_chip)
 
 static void sl28cpld_pwm_get_state(struct pwm_chip *chip,
 				   struct pwm_device *pwm,
 				   struct pwm_state *state)
 {
-	struct sl28cpld_pwm *priv = dev_get_drvdata(chip->dev);
+	struct sl28cpld_pwm *priv = sl28cpld_pwm_from_chip(chip);
 	unsigned int reg;
 	int prescaler;
 
@@ -118,7 +120,7 @@ static void sl28cpld_pwm_get_state(struct pwm_chip *chip,
 static int sl28cpld_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 			      const struct pwm_state *state)
 {
-	struct sl28cpld_pwm *priv = dev_get_drvdata(chip->dev);
+	struct sl28cpld_pwm *priv = sl28cpld_pwm_from_chip(chip);
 	unsigned int cycle, prescaler;
 	bool write_duty_cycle_first;
 	int ret;
-- 
2.29.2


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