[PATCH 4/8] pwm: Ensure a struct pwm has the same lifetime as its pwm_chip

[Uwe Kleine-König]

It's required to not free the memory underlying a requested PWM
while a consumer still has a reference to it. While currently a pwm_chip
doesn't life long enough in all cases, linking the struct pwm to the
pwm_chip results in the right lifetime as soon as the pwmchip is living
long enough. This happens with the following commits.

Note this is a breaking change for all pwm drivers that don't use
pwmchip_alloc().

Reviewed-by: Gustavo A. R. Silva <gustavo...@kernel.org> # for struct_size() 
and __counted_by()
Signed-off-by: Uwe Kleine-König <u.kleine-koe...@pengutronix.de>
---
 drivers/pwm/core.c  | 27 ++++++++++-----------------
 include/linux/pwm.h |  2 +-
 2 files changed, 11 insertions(+), 18 deletions(-)

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index 69af8123455a..8ed4c93cd0ce 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -987,7 +987,7 @@ static void pwmchip_sysfs_unexport(struct pwm_chip *chip)
 
 static void *pwmchip_priv(struct pwm_chip *chip)
 {
-       return (void *)chip + ALIGN(sizeof(*chip), PWMCHIP_ALIGN);
+       return (void *)chip + ALIGN(struct_size(chip, pwms, chip->npwm), 
PWMCHIP_ALIGN);
 }
 
 /* This is the counterpart to pwmchip_alloc() */
@@ -1001,8 +1001,10 @@ struct pwm_chip *pwmchip_alloc(struct device *parent, 
unsigned int npwm, size_t
 {
        struct pwm_chip *chip;
        size_t alloc_size;
+       unsigned int i;
 
-       alloc_size = size_add(ALIGN(sizeof(*chip), PWMCHIP_ALIGN), sizeof_priv);
+       alloc_size = size_add(ALIGN(struct_size(chip, pwms, npwm), 
PWMCHIP_ALIGN),
+                             sizeof_priv);
 
        chip = kzalloc(alloc_size, GFP_KERNEL);
        if (!chip)
@@ -1014,6 +1016,12 @@ struct pwm_chip *pwmchip_alloc(struct device *parent, 
unsigned int npwm, size_t
 
        pwmchip_set_drvdata(chip, pwmchip_priv(chip));
 
+       for (i = 0; i < chip->npwm; i++) {
+               struct pwm_device *pwm = &chip->pwms[i];
+               pwm->chip = chip;
+               pwm->hwpwm = i;
+       }
+
        return chip;
 }
 EXPORT_SYMBOL_GPL(pwmchip_alloc);
@@ -1085,7 +1093,6 @@ static bool pwm_ops_check(const struct pwm_chip *chip)
  */
 int __pwmchip_add(struct pwm_chip *chip, struct module *owner)
 {
-       unsigned int i;
        int ret;
 
        if (!chip || !pwmchip_parent(chip) || !chip->ops || !chip->npwm)
@@ -1105,28 +1112,16 @@ int __pwmchip_add(struct pwm_chip *chip, struct module 
*owner)
 
        chip->owner = owner;
 
-       chip->pwms = kcalloc(chip->npwm, sizeof(*chip->pwms), GFP_KERNEL);
-       if (!chip->pwms)
-               return -ENOMEM;
-
        mutex_lock(&pwm_lock);
 
        ret = idr_alloc(&pwm_chips, chip, 0, 0, GFP_KERNEL);
        if (ret < 0) {
                mutex_unlock(&pwm_lock);
-               kfree(chip->pwms);
                return ret;
        }
 
        chip->id = ret;
 
-       for (i = 0; i < chip->npwm; i++) {
-               struct pwm_device *pwm = &chip->pwms[i];
-
-               pwm->chip = chip;
-               pwm->hwpwm = i;
-       }
-
        mutex_unlock(&pwm_lock);
 
        if (IS_ENABLED(CONFIG_OF))
@@ -1156,8 +1151,6 @@ void pwmchip_remove(struct pwm_chip *chip)
        idr_remove(&pwm_chips, chip->id);
 
        mutex_unlock(&pwm_lock);
-
-       kfree(chip->pwms);
 }
 EXPORT_SYMBOL_GPL(pwmchip_remove);
 
diff --git a/include/linux/pwm.h b/include/linux/pwm.h
index 17e45d8413ed..78b9061572ff 100644
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -290,7 +290,7 @@ struct pwm_chip {
        /* only used internally by the PWM framework */
        bool uses_pwmchip_alloc;
        void *driver_data;
-       struct pwm_device *pwms;
+       struct pwm_device pwms[] __counted_by(npwm);
 };
 
 static inline struct device *pwmchip_parent(const struct pwm_chip *chip)
-- 
2.43.0