| Message ID | f59b1a4a8d6fba65e4d3e8698310c9cb1d4c43ce.1706182805.git.u.kleine-koenig@pengutronix.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | pwm: Improve lifetime tracking for pwm_chips | expand |
On 1/25/24 6:09 AM, Uwe Kleine-König wrote: > This function allocates a struct pwm_chip and driver data. Compared to > the status quo the split into pwm_chip and driver data is new, otherwise > it doesn't change anything relevant (yet). > > The intention is that after all drivers are switched to use this > allocation function, its possible to add a struct device to struct > pwm_chip to properly track the latter's lifetime without touching all > drivers again. Proper lifetime tracking is a necessary precondition to > introduce character device support for PWMs (that implements atomic > setting and doesn't suffer from the sysfs overhead of the /sys/class/pwm > userspace support). > > The new function pwmchip_priv() (obviously?) only works for chips > allocated with devm_pwmchip_alloc(). I think this looks good. Two questions: - Should you explicitly align the private data? Or do you believe the default alignment (currently pointer size aligned) is adequate? - Is there a non-devres version of the allocation function? -Alex > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> > --- > .../driver-api/driver-model/devres.rst | 1 + > Documentation/driver-api/pwm.rst | 10 ++++---- > drivers/pwm/core.c | 25 +++++++++++++++++++ > include/linux/pwm.h | 2 ++ > 4 files changed, 33 insertions(+), 5 deletions(-) > > diff --git a/Documentation/driver-api/driver-model/devres.rst b/Documentation/driver-api/driver-model/devres.rst > index c5f99d834ec5..e4df72c408d2 100644 > --- a/Documentation/driver-api/driver-model/devres.rst > +++ b/Documentation/driver-api/driver-model/devres.rst > @@ -420,6 +420,7 @@ POWER > devm_reboot_mode_unregister() > > PWM > + devm_pwmchip_alloc() > devm_pwmchip_add() > devm_pwm_get() > devm_fwnode_pwm_get() > diff --git a/Documentation/driver-api/pwm.rst b/Documentation/driver-api/pwm.rst > index 3c28ccc4b611..cee66c7f0335 100644 > --- a/Documentation/driver-api/pwm.rst > +++ b/Documentation/driver-api/pwm.rst > @@ -143,11 +143,11 @@ to implement the pwm_*() functions itself. This means that it's impossible > to have multiple PWM drivers in the system. For this reason it's mandatory > for new drivers to use the generic PWM framework. > > -A new PWM controller/chip can be added using pwmchip_add() and removed > -again with pwmchip_remove(). pwmchip_add() takes a filled in struct > -pwm_chip as argument which provides a description of the PWM chip, the > -number of PWM devices provided by the chip and the chip-specific > -implementation of the supported PWM operations to the framework. > +A new PWM controller/chip can be allocated using devm_pwmchip_alloc, then added > +using pwmchip_add() and removed again with pwmchip_remove(). pwmchip_add() > +takes a filled in struct pwm_chip as argument which provides a description of > +the PWM chip, the number of PWM devices provided by the chip and the > +chip-specific implementation of the supported PWM operations to the framework. > > When implementing polarity support in a PWM driver, make sure to respect the > signal conventions in the PWM framework. By definition, normal polarity > diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c > index 1b4c3d0caa82..b821a2b0b172 100644 > --- a/drivers/pwm/core.c > +++ b/drivers/pwm/core.c > @@ -454,6 +454,31 @@ of_pwm_single_xlate(struct pwm_chip *chip, const struct of_phandle_args *args) > } > EXPORT_SYMBOL_GPL(of_pwm_single_xlate); > > +static void *pwmchip_priv(struct pwm_chip *chip) > +{ > + return (void *)chip + sizeof(*chip); > +} > + > +struct pwm_chip *devm_pwmchip_alloc(struct device *parent, unsigned int npwm, size_t sizeof_priv) > +{ > + struct pwm_chip *chip; > + size_t alloc_size; > + > + alloc_size = size_add(sizeof(*chip), sizeof_priv); > + > + chip = devm_kzalloc(parent, alloc_size, GFP_KERNEL); > + if (!chip) > + return ERR_PTR(-ENOMEM); > + > + chip->dev = parent; > + chip->npwm = npwm; > + > + pwmchip_set_drvdata(chip, pwmchip_priv(chip)); > + > + return chip; > +} > +EXPORT_SYMBOL_GPL(devm_pwmchip_alloc); > + > static void of_pwmchip_add(struct pwm_chip *chip) > { > if (!chip->dev || !chip->dev->of_node) > diff --git a/include/linux/pwm.h b/include/linux/pwm.h > index 2c49d2fe2fe7..8bc7504aa7d4 100644 > --- a/include/linux/pwm.h > +++ b/include/linux/pwm.h > @@ -403,6 +403,8 @@ static inline bool pwm_might_sleep(struct pwm_device *pwm) > int pwm_capture(struct pwm_device *pwm, struct pwm_capture *result, > unsigned long timeout); > > +struct pwm_chip *devm_pwmchip_alloc(struct device *parent, unsigned int npwm, size_t sizeof_priv); > + > int __pwmchip_add(struct pwm_chip *chip, struct module *owner); > #define pwmchip_add(chip) __pwmchip_add(chip, THIS_MODULE) > void pwmchip_remove(struct pwm_chip *chip);
Hello Alex, On Fri, Jan 26, 2024 at 08:56:33AM -0600, Alex Elder wrote: > On 1/25/24 6:09 AM, Uwe Kleine-König wrote: > > This function allocates a struct pwm_chip and driver data. Compared to > > the status quo the split into pwm_chip and driver data is new, otherwise > > it doesn't change anything relevant (yet). > > > > The intention is that after all drivers are switched to use this > > allocation function, its possible to add a struct device to struct > > pwm_chip to properly track the latter's lifetime without touching all > > drivers again. Proper lifetime tracking is a necessary precondition to > > introduce character device support for PWMs (that implements atomic > > setting and doesn't suffer from the sysfs overhead of the /sys/class/pwm > > userspace support). > > > > The new function pwmchip_priv() (obviously?) only works for chips > > allocated with devm_pwmchip_alloc(). > > I think this looks good. Two questions: > - Should you explicitly align the private data? Or do you believe > the default alignment (currently pointer size aligned) is adequate? I'm not aware of a requirement for a higher order alignment (but I might well miss something). I did my tests on arm, nothing exploded there. Maybe the conservative approach of asserting the same alignment as kmalloc would be a good idea. I'll think and research about that. iio uses ARCH_DMA_MINALIGN, net uses 32 (NETDEV_ALIGN). > - Is there a non-devres version of the allocation function? Patch #109 introduces a non-devres variant. As it's not used it's a static function though. Can easily be changed is a use case pops up. Best regards Uwe
diff --git a/Documentation/driver-api/driver-model/devres.rst b/Documentation/driver-api/driver-model/devres.rst index c5f99d834ec5..e4df72c408d2 100644 --- a/Documentation/driver-api/driver-model/devres.rst +++ b/Documentation/driver-api/driver-model/devres.rst @@ -420,6 +420,7 @@ POWER devm_reboot_mode_unregister() PWM + devm_pwmchip_alloc() devm_pwmchip_add() devm_pwm_get() devm_fwnode_pwm_get() diff --git a/Documentation/driver-api/pwm.rst b/Documentation/driver-api/pwm.rst index 3c28ccc4b611..cee66c7f0335 100644 --- a/Documentation/driver-api/pwm.rst +++ b/Documentation/driver-api/pwm.rst @@ -143,11 +143,11 @@ to implement the pwm_*() functions itself. This means that it's impossible to have multiple PWM drivers in the system. For this reason it's mandatory for new drivers to use the generic PWM framework. -A new PWM controller/chip can be added using pwmchip_add() and removed -again with pwmchip_remove(). pwmchip_add() takes a filled in struct -pwm_chip as argument which provides a description of the PWM chip, the -number of PWM devices provided by the chip and the chip-specific -implementation of the supported PWM operations to the framework. +A new PWM controller/chip can be allocated using devm_pwmchip_alloc, then added +using pwmchip_add() and removed again with pwmchip_remove(). pwmchip_add() +takes a filled in struct pwm_chip as argument which provides a description of +the PWM chip, the number of PWM devices provided by the chip and the +chip-specific implementation of the supported PWM operations to the framework. When implementing polarity support in a PWM driver, make sure to respect the signal conventions in the PWM framework. By definition, normal polarity diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c index 1b4c3d0caa82..b821a2b0b172 100644 --- a/drivers/pwm/core.c +++ b/drivers/pwm/core.c @@ -454,6 +454,31 @@ of_pwm_single_xlate(struct pwm_chip *chip, const struct of_phandle_args *args) } EXPORT_SYMBOL_GPL(of_pwm_single_xlate); +static void *pwmchip_priv(struct pwm_chip *chip) +{ + return (void *)chip + sizeof(*chip); +} + +struct pwm_chip *devm_pwmchip_alloc(struct device *parent, unsigned int npwm, size_t sizeof_priv) +{ + struct pwm_chip *chip; + size_t alloc_size; + + alloc_size = size_add(sizeof(*chip), sizeof_priv); + + chip = devm_kzalloc(parent, alloc_size, GFP_KERNEL); + if (!chip) + return ERR_PTR(-ENOMEM); + + chip->dev = parent; + chip->npwm = npwm; + + pwmchip_set_drvdata(chip, pwmchip_priv(chip)); + + return chip; +} +EXPORT_SYMBOL_GPL(devm_pwmchip_alloc); + static void of_pwmchip_add(struct pwm_chip *chip) { if (!chip->dev || !chip->dev->of_node) diff --git a/include/linux/pwm.h b/include/linux/pwm.h index 2c49d2fe2fe7..8bc7504aa7d4 100644 --- a/include/linux/pwm.h +++ b/include/linux/pwm.h @@ -403,6 +403,8 @@ static inline bool pwm_might_sleep(struct pwm_device *pwm) int pwm_capture(struct pwm_device *pwm, struct pwm_capture *result, unsigned long timeout); +struct pwm_chip *devm_pwmchip_alloc(struct device *parent, unsigned int npwm, size_t sizeof_priv); + int __pwmchip_add(struct pwm_chip *chip, struct module *owner); #define pwmchip_add(chip) __pwmchip_add(chip, THIS_MODULE) void pwmchip_remove(struct pwm_chip *chip);
This function allocates a struct pwm_chip and driver data. Compared to the status quo the split into pwm_chip and driver data is new, otherwise it doesn't change anything relevant (yet). The intention is that after all drivers are switched to use this allocation function, its possible to add a struct device to struct pwm_chip to properly track the latter's lifetime without touching all drivers again. Proper lifetime tracking is a necessary precondition to introduce character device support for PWMs (that implements atomic setting and doesn't suffer from the sysfs overhead of the /sys/class/pwm userspace support). The new function pwmchip_priv() (obviously?) only works for chips allocated with devm_pwmchip_alloc(). Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> --- .../driver-api/driver-model/devres.rst | 1 + Documentation/driver-api/pwm.rst | 10 ++++---- drivers/pwm/core.c | 25 +++++++++++++++++++ include/linux/pwm.h | 2 ++ 4 files changed, 33 insertions(+), 5 deletions(-)