[PATCH v3 000/108] pwm: Fix lifetime issues for pwm_chips

[PATCH v3 000/108] pwm: Fix lifetime issues for pwm_chips

[Uwe Kleine-König]

Hello,

this is v3 of the series improving life-time tracking for PWM chips. The
urgency is gone as device links now work as expected and so all
in-kernel users are fine since commit 2e84dc379200 ("driver core:
Release all resources during unbind before updating device links").

However proper lifetime tracking is a precondition to have robust
character device support, as we cannot kill a userspace process if the
used pwm driver goes away.

Changes since v2:

 - Cc: the relevant maintainers for wider testing/review audience
 - Rebase to v6.7-rc1 + https://lore.kernel.org/linux-pwm/20231121112029.gyv3gqirlycysyr4@pengutronix.de
 - Improvements for things pointed out during review and my own
   findings here and there.
 - Implementation for a few more ioctls in the WIP commit that adds
   character support

To go forward I'd like to get in patches up to #103 (i.e. adding
pwmchip_parent() (#2), devm_pwmchip_alloc() (#37) and the conversions of
the drivers to make use of these additions).

The few commits that touch drivers not living in drivers/pwm (i.e. #36,
#100-#103) can go in either via the pwm tree with the rest, or later
---when the used functions are in---via their trees.

After all in-tree drivers are prepared with the patches up to #103, we
can think about when and how we go on with the remaining bits.

Note that patch #104 breaks all drivers that don't use
devm_pwmchip_alloc(), so this is the commit that needs coordination with the
maintainers of

 drivers/gpio/gpio-mvebu.c
 drivers/gpu/drm/bridge/ti-sn65dsi86.c
 drivers/leds/rgb/leds-qcom-lpg.c
 drivers/staging/greybus/pwm.c

The motivation for this series is the last patch. It allows to control a
pwm device via ioctl. Compared to the sysfs API this already now has
some advantages:

- It changes all parameters in a single call.
  This simplifies things similar to the introduction of
  pwm_apply_state(). With sysfs it can happen that you want to
  switch polarity but that's refused because 

	pwm_get_state(mypwm, &state);
	state.polarity = new_value;

  sometimes yield an invalid state, e.g. because state.period is
  in some cases 0 after bootup. Theoretically it can even happen that you have
  to change two parameters before reaching an applicable state, then you're
  stuck with sysfs.

- It's faster than sysfs. In my measurements with stm32 about a factor
  4.

A userspace lib to make use of this can be found at
https://git.kernel.org/pub/scm/linux/kernel/git/ukleinek/libpwm.git/ .
It makes use of the character devices if available and falls back to
sysfs. So it's somewhat useful already now.

Best regards
Uwe

Uwe Kleine-König (108):
  pwm: cros-ec: Change prototype of helper to prepare further changes
  pwm: Provide a macro to get the parent device of a given chip
  pwm: ab8500: Make use of pwmchip_parent() macro
  pwm: atmel: Make use of pwmchip_parent() macro
  pwm: atmel-tcb: Make use of pwmchip_parent() macro
  pwm: bcm-kona: Make use of pwmchip_parent() macro
  pwm: crc: Make use of pwmchip_parent() macro
  pwm: cros-ec: Make use of pwmchip_parent() macro
  pwm: dwc: Make use of pwmchip_parent() macro
  pwm: ep93xx: Make use of pwmchip_parent() macro
  pwm: fsl-ftm: Make use of pwmchip_parent() macro
  pwm: img: Make use of parent device pointer in driver data
  pwm: imx27: Make use of pwmchip_parent() macro
  pwm: jz4740: Make use of pwmchip_parent() macro
  pwm: lpc18xx-sct: Make use of parent device pointer in driver data
  pwm: lpss: Make use of pwmchip_parent() macro
  pwm: mediatek: Make use of pwmchip_parent() macro
  pwm: meson: Make use of pwmchip_parent() macro
  pwm: mtk-disp: Make use of pwmchip_parent() macro
  pwm: omap: Make use of pwmchip_parent() macro
  pwm: pca9685: Store parent device in driver data
  pwm: raspberrypi-poe: Make use of pwmchip_parent() macro
  pwm: rcar: Make use of pwmchip_parent() macro
  pwm: rz-mtu3: Make use of pwmchip_parent() macro
  pwm: samsung: Make use of pwmchip_parent() macro
  pwm: sifive: Make use of pwmchip_parent() macro
  pwm: stm32-lp: Make use of pwmchip_parent() macro
  pwm: stm32: Make use of pwmchip_parent() macro
  pwm: stmpe: Make use of pwmchip_parent() macro
  pwm: sun4i: Make use of pwmchip_parent() macro
  pwm: tiecap: Make use of pwmchip_parent() macro
  pwm: tiehrpwm: Make use of pwmchip_parent() macro
  pwm: twl-led: Make use of pwmchip_parent() macro
  pwm: twl: Make use of pwmchip_parent() macro
  pwm: vt8500: Make use of pwmchip_parent() macro
  staging: greybus: pwm: Make use of pwmchip_parent() macro
  pwm: Provide devm_pwmchip_alloc() function
  pwm: ab8500: Make use of devm_pwmchip_alloc() function
  pwm: apple: Make use of devm_pwmchip_alloc() function
  pwm: atmel-hlcdc: Make use of devm_pwmchip_alloc() function
  pwm: atmel: Make use of devm_pwmchip_alloc() function
  pwm: atmel-tcb: Make use of devm_pwmchip_alloc() function
  pwm: bcm2835: Make use of devm_pwmchip_alloc() function
  pwm: bcm-iproc: Make use of devm_pwmchip_alloc() function
  pwm: bcm-kona: Make use of devm_pwmchip_alloc() function
  pwm: berlin: Make use of devm_pwmchip_alloc() function
  pwm: brcmstb: Make use of devm_pwmchip_alloc() function
  pwm: clk: Make use of devm_pwmchip_alloc() function
  pwm: clps711x: Make use of devm_pwmchip_alloc() function
  pwm: crc: Make use of devm_pwmchip_alloc() function
  pwm: cros-ec: Make use of devm_pwmchip_alloc() function
  pwm: dwc: Make use of devm_pwmchip_alloc() function
  pwm: ep93xx: Make use of devm_pwmchip_alloc() function
  pwm: fsl-ftm: Make use of devm_pwmchip_alloc() function
  pwm: hibvt: Make use of devm_pwmchip_alloc() function
  pwm: img: Make use of devm_pwmchip_alloc() function
  pwm: imx1: Make use of devm_pwmchip_alloc() function
  pwm: imx27: Make use of devm_pwmchip_alloc() function
  pwm: imx-tpm: Make use of devm_pwmchip_alloc() function
  pwm: intel-lgm: Make use of devm_pwmchip_alloc() function
  pwm: iqs620a: Make use of devm_pwmchip_alloc() function
  pwm: jz4740: Make use of devm_pwmchip_alloc() function
  pwm: keembay: Make use of devm_pwmchip_alloc() function
  pwm: lp3943: Make use of devm_pwmchip_alloc() function
  pwm: lpc18xx-sct: Make use of devm_pwmchip_alloc() function
  pwm: lpc32xx: Make use of devm_pwmchip_alloc() function
  pwm: lpss-*: Make use of devm_pwmchip_alloc() function
  pwm: mediatek: Make use of devm_pwmchip_alloc() function
  pwm: meson: Make use of devm_pwmchip_alloc() function
  pwm: microchip-core: Make use of devm_pwmchip_alloc() function
  pwm: mtk-disp: Make use of devm_pwmchip_alloc() function
  pwm: mxs: Make use of devm_pwmchip_alloc() function
  pwm: ntxec: Make use of devm_pwmchip_alloc() function
  pwm: omap-dmtimer: Make use of devm_pwmchip_alloc() function
  pwm: pca9685: Make use of devm_pwmchip_alloc() function
  pwm: pxa: Make use of devm_pwmchip_alloc() function
  pwm: raspberrypi-poe: Make use of devm_pwmchip_alloc() function
  pwm: rcar: Make use of devm_pwmchip_alloc() function
  pwm: renesas-tpu: Make use of devm_pwmchip_alloc() function
  pwm: rockchip: Make use of devm_pwmchip_alloc() function
  pwm: rz-mtu3: Make use of devm_pwmchip_alloc() function
  pwm: samsung: Make use of devm_pwmchip_alloc() function
  pwm: sifive: Make use of devm_pwmchip_alloc() function
  pwm: sl28cpld: Make use of devm_pwmchip_alloc() function
  pwm: spear: Make use of devm_pwmchip_alloc() function
  pwm: sprd: Make use of devm_pwmchip_alloc() function
  pwm: sti: Make use of devm_pwmchip_alloc() function
  pwm: stm32-lp: Make use of devm_pwmchip_alloc() function
  pwm: stm32: Make use of devm_pwmchip_alloc() function
  pwm: stmpe: Make use of devm_pwmchip_alloc() function
  pwm: sun4i: Make use of devm_pwmchip_alloc() function
  pwm: sunplus: Make use of devm_pwmchip_alloc() function
  pwm: tegra: Make use of devm_pwmchip_alloc() function
  pwm: tiecap: Make use of devm_pwmchip_alloc() function
  pwm: twl-led: Make use of devm_pwmchip_alloc() function
  pwm: twl: Make use of devm_pwmchip_alloc() function
  pwm: visconti: Make use of devm_pwmchip_alloc() function
  pwm: vt8500: Make use of devm_pwmchip_alloc() function
  pwm: xilinx: Make use of devm_pwmchip_alloc() function
  gpio: mvebu: Make use of devm_pwmchip_alloc() function
  drm/bridge: ti-sn65dsi86: Make use of devm_pwmchip_alloc() function
  leds: qcom-lpg: Make use of devm_pwmchip_alloc() function
  staging: greybus: pwm: Make use of devm_pwmchip_alloc() function
  pwm: Ensure that pwm_chips are allocated using pwmchip_alloc()
  pwm: Ensure a struct pwm has the same lifetime as its pwm_chip
  pwm: Ensure the memory backing a PWM chip isn't freed while used
  pwm: Add more locking
  WIP: pwm: Add support for pwmchip devices for faster and easier
    userspace access

 .../driver-api/driver-model/devres.rst        |   1 +
 Documentation/driver-api/pwm.rst              |  10 +-
 drivers/gpio/gpio-mvebu.c                     |  18 +-
 drivers/gpu/drm/bridge/ti-sn65dsi86.c         |  25 +-
 drivers/leds/rgb/leds-qcom-lpg.c              |  30 +-
 drivers/pwm/Kconfig                           |   4 -
 drivers/pwm/Makefile                          |   3 +-
 drivers/pwm/core.c                            | 480 +++++++++++++++---
 drivers/pwm/pwm-ab8500.c                      |  36 +-
 drivers/pwm/pwm-apple.c                       |  18 +-
 drivers/pwm/pwm-atmel-hlcdc.c                 |  35 +-
 drivers/pwm/pwm-atmel-tcb.c                   |  26 +-
 drivers/pwm/pwm-atmel.c                       |  37 +-
 drivers/pwm/pwm-bcm-iproc.c                   |  19 +-
 drivers/pwm/pwm-bcm-kona.c                    |  21 +-
 drivers/pwm/pwm-bcm2835.c                     |  17 +-
 drivers/pwm/pwm-berlin.c                      |  29 +-
 drivers/pwm/pwm-brcmstb.c                     |  17 +-
 drivers/pwm/pwm-clk.c                         |  27 +-
 drivers/pwm/pwm-clps711x.c                    |  21 +-
 drivers/pwm/pwm-crc.c                         |  26 +-
 drivers/pwm/pwm-cros-ec.c                     |  51 +-
 drivers/pwm/pwm-dwc-core.c                    |  25 +-
 drivers/pwm/pwm-dwc.c                         |  18 +-
 drivers/pwm/pwm-dwc.h                         |   9 +-
 drivers/pwm/pwm-ep93xx.c                      |  21 +-
 drivers/pwm/pwm-fsl-ftm.c                     |  48 +-
 drivers/pwm/pwm-hibvt.c                       |  25 +-
 drivers/pwm/pwm-img.c                         |  51 +-
 drivers/pwm/pwm-imx-tpm.c                     |  34 +-
 drivers/pwm/pwm-imx1.c                        |  17 +-
 drivers/pwm/pwm-imx27.c                       |  26 +-
 drivers/pwm/pwm-intel-lgm.c                   |  17 +-
 drivers/pwm/pwm-iqs620a.c                     |  37 +-
 drivers/pwm/pwm-jz4740.c                      |  35 +-
 drivers/pwm/pwm-keembay.c                     |  17 +-
 drivers/pwm/pwm-lp3943.c                      |  17 +-
 drivers/pwm/pwm-lpc18xx-sct.c                 |  35 +-
 drivers/pwm/pwm-lpc32xx.c                     |  19 +-
 drivers/pwm/pwm-lpss-pci.c                    |  10 +-
 drivers/pwm/pwm-lpss-platform.c               |  10 +-
 drivers/pwm/pwm-lpss.c                        |  34 +-
 drivers/pwm/pwm-lpss.h                        |   1 -
 drivers/pwm/pwm-mediatek.c                    |  28 +-
 drivers/pwm/pwm-meson.c                       |  57 ++-
 drivers/pwm/pwm-microchip-core.c              |  17 +-
 drivers/pwm/pwm-mtk-disp.c                    |  25 +-
 drivers/pwm/pwm-mxs.c                         |  32 +-
 drivers/pwm/pwm-ntxec.c                       |  30 +-
 drivers/pwm/pwm-omap-dmtimer.c                |  46 +-
 drivers/pwm/pwm-pca9685.c                     |  98 ++--
 drivers/pwm/pwm-pxa.c                         |  21 +-
 drivers/pwm/pwm-raspberrypi-poe.c             |  20 +-
 drivers/pwm/pwm-rcar.c                        |  25 +-
 drivers/pwm/pwm-renesas-tpu.c                 |  18 +-
 drivers/pwm/pwm-rockchip.c                    |  24 +-
 drivers/pwm/pwm-rz-mtu3.c                     |  38 +-
 drivers/pwm/pwm-samsung.c                     |  56 +-
 drivers/pwm/pwm-sifive.c                      |  30 +-
 drivers/pwm/pwm-sl28cpld.c                    |  13 +-
 drivers/pwm/pwm-spear.c                       |  17 +-
 drivers/pwm/pwm-sprd.c                        |  50 +-
 drivers/pwm/pwm-sti.c                         |  34 +-
 drivers/pwm/pwm-stm32-lp.c                    |  29 +-
 drivers/pwm/pwm-stm32.c                       |  53 +-
 drivers/pwm/pwm-stmpe.c                       |  58 ++-
 drivers/pwm/pwm-sun4i.c                       |  38 +-
 drivers/pwm/pwm-sunplus.c                     |  17 +-
 drivers/pwm/pwm-tegra.c                       |  27 +-
 drivers/pwm/pwm-tiecap.c                      |  55 +-
 drivers/pwm/pwm-tiehrpwm.c                    |  72 +--
 drivers/pwm/pwm-twl-led.c                     |  58 ++-
 drivers/pwm/pwm-twl.c                         |  50 +-
 drivers/pwm/pwm-visconti.c                    |  17 +-
 drivers/pwm/pwm-vt8500.c                      |  41 +-
 drivers/pwm/pwm-xilinx.c                      |  34 +-
 drivers/pwm/sysfs.c                           |  64 +--
 drivers/staging/greybus/pwm.c                 | 130 ++---
 include/linux/platform_data/x86/pwm-lpss.h    |   4 +-
 include/linux/pwm.h                           |  36 +-
 include/uapi/linux/pwm.h                      |  23 +
 81 files changed, 1651 insertions(+), 1291 deletions(-)
 create mode 100644 include/uapi/linux/pwm.h

base-commit: 869de350ff3834145273a6d39faedea878c6715a
-- 
2.42.0

[PATCH v3 105/108] 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().

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
---
 drivers/pwm/core.c  | 26 ++++++++++----------------
 include/linux/pwm.h |  2 +-
 2 files changed, 11 insertions(+), 17 deletions(-)

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index 15942210aa08..029aa1c69591 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -198,7 +198,7 @@ static bool pwm_ops_check(const struct pwm_chip *chip)
 
 void *pwmchip_priv(struct pwm_chip *chip)
 {
-	return (void *)chip + sizeof(*chip);
+	return (void *)chip + struct_size(chip, pwms, chip->npwm);
 }
 EXPORT_SYMBOL_GPL(pwmchip_priv);
 
@@ -206,8 +206,9 @@ struct pwm_chip *devm_pwmchip_alloc(struct device *parent, unsigned int npwm, si
 {
 	struct pwm_chip *chip;
 	size_t alloc_size;
+	unsigned int i;
 
-	alloc_size = size_add(sizeof(*chip), sizeof_priv);
+	alloc_size = size_add(struct_size(chip, pwms, npwm), sizeof_priv);
 
 	chip = devm_kzalloc(parent, alloc_size, GFP_KERNEL);
 	if (!chip)
@@ -217,6 +218,13 @@ struct pwm_chip *devm_pwmchip_alloc(struct device *parent, unsigned int npwm, si
 	chip->npwm = npwm;
 	chip->uses_pwmchip_alloc = true;
 
+	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(devm_pwmchip_alloc);
@@ -234,7 +242,6 @@ EXPORT_SYMBOL_GPL(devm_pwmchip_alloc);
 int __pwmchip_add(struct pwm_chip *chip, struct module *owner)
 {
 	int ret;
-	unsigned i;
 
 	if (!chip || !chip->dev || !chip->ops || !chip->npwm)
 		return -EINVAL;
@@ -253,26 +260,15 @@ 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(&pwmchip_idr, 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);
 
@@ -303,8 +299,6 @@ void pwmchip_remove(struct pwm_chip *chip)
 	idr_remove(&pwmchip_idr, 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 b8e70ee01d31..a7294ef1495d 100644
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -302,7 +302,7 @@ struct pwm_chip {
 
 	/* only used internally by the PWM framework */
 	bool uses_pwmchip_alloc;
-	struct pwm_device *pwms;
+	struct pwm_device pwms[] __counted_by(npwm);
 };
 
 static inline struct device *pwmchip_parent(struct pwm_chip *chip)
-- 
2.42.0

Re: [PATCH v3 105/108] pwm: Ensure a struct pwm has the same lifetime as its pwm_chip

[Gustavo A. R. Silva]

On 11/21/23 07:50, Uwe Kleine-König wrote:
> 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().
> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org> # for struct_size() and __counted_by()

Thanks for including __counted_by(). :)
--
Gustavo

> ---
>   drivers/pwm/core.c  | 26 ++++++++++----------------
>   include/linux/pwm.h |  2 +-
>   2 files changed, 11 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 15942210aa08..029aa1c69591 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -198,7 +198,7 @@ static bool pwm_ops_check(const struct pwm_chip *chip)
>   
>   void *pwmchip_priv(struct pwm_chip *chip)
>   {
> -	return (void *)chip + sizeof(*chip);
> +	return (void *)chip + struct_size(chip, pwms, chip->npwm);
>   }
>   EXPORT_SYMBOL_GPL(pwmchip_priv);
>   
> @@ -206,8 +206,9 @@ struct pwm_chip *devm_pwmchip_alloc(struct device *parent, unsigned int npwm, si
>   {
>   	struct pwm_chip *chip;
>   	size_t alloc_size;
> +	unsigned int i;
>   
> -	alloc_size = size_add(sizeof(*chip), sizeof_priv);
> +	alloc_size = size_add(struct_size(chip, pwms, npwm), sizeof_priv);
>   
>   	chip = devm_kzalloc(parent, alloc_size, GFP_KERNEL);
>   	if (!chip)
> @@ -217,6 +218,13 @@ struct pwm_chip *devm_pwmchip_alloc(struct device *parent, unsigned int npwm, si
>   	chip->npwm = npwm;
>   	chip->uses_pwmchip_alloc = true;
>   
> +	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(devm_pwmchip_alloc);
> @@ -234,7 +242,6 @@ EXPORT_SYMBOL_GPL(devm_pwmchip_alloc);
>   int __pwmchip_add(struct pwm_chip *chip, struct module *owner)
>   {
>   	int ret;
> -	unsigned i;
>   
>   	if (!chip || !chip->dev || !chip->ops || !chip->npwm)
>   		return -EINVAL;
> @@ -253,26 +260,15 @@ 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(&pwmchip_idr, 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);
>   
> @@ -303,8 +299,6 @@ void pwmchip_remove(struct pwm_chip *chip)
>   	idr_remove(&pwmchip_idr, 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 b8e70ee01d31..a7294ef1495d 100644
> --- a/include/linux/pwm.h
> +++ b/include/linux/pwm.h
> @@ -302,7 +302,7 @@ struct pwm_chip {
>   
>   	/* only used internally by the PWM framework */
>   	bool uses_pwmchip_alloc;
> -	struct pwm_device *pwms;
> +	struct pwm_device pwms[] __counted_by(npwm);
>   };
>   
>   static inline struct device *pwmchip_parent(struct pwm_chip *chip)