[PATCH v2 02/10] pwm: Allow chips to support multiple PWMs.
Ryan Mallon
rmallon at gmail.com
Tue Feb 7 17:53:23 EST 2012
On 07/02/12 02:19, Thierry Reding wrote:
Hi Thierry,
A few comments below,
~Ryan
> This commit modifies the PWM core to support multiple PWMs per struct
> pwm_chip. It achieves this in a similar way to how gpiolib works, by
> allowing PWM ranges to be requested dynamically (pwm_chip.base == -1) or
> starting at a given offset (pwm_chip.base >= 0). A chip specifies how
> many PWMs it controls using the npwm member. Each of the functions in
> the pwm_ops structure gets an additional argument that specified the PWM
> number (it can be converted to a per-chip index by subtracting the
> chip's base).
>
> The total maximum number of PWM devices is currently fixed to 64, but
> can easily be made configurable via Kconfig.
It would be better to make the code handle arbitrary numbers of PWMs. A
Kconfig knob becomes annoying when you have more than one platform
configured into the kernel.
> The patch is incomplete in that it doesn't convert any existing drivers
> that are now broken.
Does this patch actually break the drivers in terms of not building or
running? If so, can this patch series be reworked a bit to allow the old
PWM framework to be used until all of the drivers are converted?
>
> Signed-off-by: Thierry Reding <thierry.reding at avionic-design.de>
> ---
> Changes in v2:
> - add 'struct device *dev' field to pwm_chip, drop label field
> - use radix tree for PWM descriptors
> - add pwm_set_chip_data() and pwm_get_chip_data() functions to allow
> storing and retrieving chip-specific per-PWM data
>
> TODO:
> - pass chip-indexed PWM number (PWM descriptor?) to drivers
> - merge with Sascha's patch
>
> drivers/pwm/core.c | 287 ++++++++++++++++++++++++++++++++++++++-------------
> include/linux/pwm.h | 37 +++++--
> 2 files changed, 242 insertions(+), 82 deletions(-)
>
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 71de479..a223bd6 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -17,154 +17,292 @@
> * along with this program; see the file COPYING. If not, write to
> * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
> */
> +
> #include <linux/module.h>
> +#include <linux/of_pwm.h>
> #include <linux/pwm.h>
> +#include <linux/radix-tree.h>
> #include <linux/list.h>
> #include <linux/mutex.h>
> #include <linux/err.h>
> #include <linux/slab.h>
> #include <linux/device.h>
>
> +#define MAX_PWMS 1024
> +
> struct pwm_device {
> - struct pwm_chip *chip;
> - const char *label;
> + const char *label;
> + unsigned int pwm;
> +};
> +
> +struct pwm_desc {
> + struct pwm_chip *chip;
> + void *chip_data;
> unsigned long flags;
> #define FLAG_REQUESTED 0
> #define FLAG_ENABLED 1
> - struct list_head node;
> + struct pwm_device pwm;
> };
Do pwm_desc and pwm_device really need to be separate structs?
pwm_device only has two fields, which could easily be added to pwm_desc
(and rename it to pmw_device if you like). They are both opaque
structures, so it makes no difference to the users of the framework.
> -static LIST_HEAD(pwm_list);
> -
> static DEFINE_MUTEX(pwm_lock);
> +static DECLARE_BITMAP(allocated_pwms, MAX_PWMS);
> +static RADIX_TREE(pwm_desc_tree, GFP_KERNEL);
I missed any discussion of this from v1, but why was this approach
chosen? The bitmap arbitrarily limits the maximum number of PWMs and is
also a little bit (nitpicky) wasteful when a platform doesn't need
anywhere near 1024 PWMs.
In most cases I would expect that platforms only have a handful of PWMs
(say less than 32), in which case a list lookup isn't too bad.
As someone else mentioned, it might be best to drop the global numbering
scheme and have each pwm_chip have its own numbering for its PWMs. So
requesting a PWM would first require getting a handle to the PWM chip it
is on. If a chip has a fixed number of PWMs (e.g. set a registration
time) then the PWMs within a chip can just be an array with O(1) lookup.
> +static struct pwm_desc *pwm_to_desc(unsigned int pwm)
> +{
> + return radix_tree_lookup(&pwm_desc_tree, pwm);
> +}
> +
> +static struct pwm_desc *alloc_desc(unsigned int pwm)
> +{
> + struct pwm_desc *desc;
> +
> + desc = kzalloc(sizeof(*desc), GFP_KERNEL);
> + if (!desc)
> + return NULL;
>
> -static struct pwm_device *_find_pwm(int pwm_id)
> + return desc;
> +}
> +
> +static void free_desc(unsigned int pwm)
> +{
> + struct pwm_desc *desc = pwm_to_desc(pwm);
> +
> + radix_tree_delete(&pwm_desc_tree, pwm);
> + kfree(desc);
> +}
> +
> +static int alloc_descs(int pwm, unsigned int from, unsigned int count)
> {
You don't really need the from argument. There is only one caller for
alloc_descs and it passes 0 for from. So you could re-write this as:
static int alloc_descs(int pwm, unsigned int count)
{
unsigned int from = 0;
...
if (pwm > MAX_PWMS)
return -EINVAL;
if (pwm >= 0)
from = pwm;
> - struct pwm_device *pwm;
> + unsigned int start;
> + unsigned int i;
> + int ret = 0;
> +
> + if (pwm >= 0) {
> + if (from > pwm)
> + return -EINVAL;
> +
> + from = pwm;
> + }
This doesn't catch some caller errors:
if (pwm > MAX_PWMS || from > MAX_PWMS)
return -EINVAL;
> +
> + start = bitmap_find_next_zero_area(allocated_pwms, MAX_PWMS, from,
> + count, 0);
Do the PWM indexes need to be contiguous for a given PWM chip? You could
probably grab each bit individually. That said, I think a better
solution is to have per-chip numbering.
> - list_for_each_entry(pwm, &pwm_list, node) {
> - if (pwm->chip->pwm_id == pwm_id)
> - return pwm;
> + if ((pwm >= 0) && (start != pwm))
Don't need the inner parens.
> + return -EEXIST;
> +
> + if (start + count > MAX_PWMS)
> + return -ENOSPC;
Is this possible? Can bitmap_find_next_zero_area return a start position
where the count would exceed the maximum?
> +
> + for (i = start; i < start + count; i++) {
> + struct pwm_desc *desc = alloc_desc(i);
> + if (!desc) {
> + ret = -ENOMEM;
> + goto err;
> + }
> +
> + radix_tree_insert(&pwm_desc_tree, i, desc);
> }
>
> - return NULL;
> + bitmap_set(allocated_pwms, start, count);
> +
> + return start;
> +
> +err:
> + for (i--; i >= 0; i--)
Nitpick:
while (--i >= 0)
is a bit simpler.
> + free_desc(i);
> +
> + return ret;
> +}
> +
> +static void free_descs(unsigned int from, unsigned int count)
> +{
> + unsigned int i;
> +
> + for (i = from; i < from + count; i++)
> + free_desc(i);
> +
> + bitmap_clear(allocated_pwms, from, count);
> }
>
> /**
> - * pwmchip_add() - register a new pwm
> - * @chip: the pwm
> - *
> - * register a new pwm. pwm->pwm_id must be initialized. if pwm_id < 0 then
> - * a dynamically assigned id will be used, otherwise the id specified,
> + * pwm_set_chip_data - set private chip data for a PWM
> + * @pwm: PWM number
> + * @data: pointer to chip-specific data
> */
> -int pwmchip_add(struct pwm_chip *chip)
> +int pwm_set_chip_data(unsigned int pwm, void *data)
This interface is a bit ugly. Shouldn't the user need to have a handle
to the pwm_device in order to access the chip_data? Why should callers
be able to set/grab chip data from random PWMs?
> {
> - struct pwm_device *pwm;
> - int ret = 0;
> + struct pwm_desc *desc = pwm_to_desc(pwm);
>
> - pwm = kzalloc(sizeof(*pwm), GFP_KERNEL);
> - if (!pwm)
> - return -ENOMEM;
> + if (!desc)
> + return -EINVAL;
>
> - pwm->chip = chip;
> + desc->chip_data = data;
> + return 0;
> +}
> +
> +/**
> + * pwm_get_chip_data - get private chip data for a PWM
> + * @pwm: PWM number
> + */
> +void *pwm_get_chip_data(unsigned int pwm)
> +{
> + struct pwm_desc *desc = pwm_to_desc(pwm);
> +
> + return desc ? desc->chip_data : NULL;
> +}
> +
> +/**
> + * pwmchip_add() - register a new PWM chip
> + * @chip: the PWM chip to add
> + *
> + * Register a new PWM chip. If pwm->base < 0 then a dynamically assigned base
> + * will be used.
> + */
> +int pwmchip_add(struct pwm_chip *chip)
> +{
> + unsigned int i;
> + int ret;
>
> mutex_lock(&pwm_lock);
>
> - if (chip->pwm_id >= 0 && _find_pwm(chip->pwm_id)) {
> - ret = -EBUSY;
> + ret = alloc_descs(chip->base, 0, chip->npwm);
> + if (ret < 0)
> goto out;
> +
> + chip->base = ret;
> + ret = 0;
> +
> + /* initialize descriptors */
> + for (i = chip->base; i < chip->base + chip->npwm; i++) {
> + struct pwm_desc *desc = pwm_to_desc(i);
> +
> + if (!desc) {
> + pr_debug("pwm: descriptor %u not initialized\n", i);
Should this be a WARN_ON?
> + continue;
> + }
> +
> + desc->chip = chip;
> }
>
> - list_add_tail(&pwm->node, &pwm_list);
> + of_pwmchip_add(chip);
> +
> out:
> mutex_unlock(&pwm_lock);
> -
> - if (ret)
> - kfree(pwm);
> -
> return ret;
> }
> EXPORT_SYMBOL_GPL(pwmchip_add);
>
> /**
> - * pwmchip_remove() - remove a pwm
> - * @chip: the pwm
> + * pwmchip_remove() - remove a PWM chip
> + * @chip: the PWM chip to remove
> *
> - * remove a pwm. This function may return busy if the pwm is still requested.
> + * Removes a PWM chip. This function may return busy if the PWM chip provides
> + * a PWM device that is still requested.
> */
> int pwmchip_remove(struct pwm_chip *chip)
> {
> - struct pwm_device *pwm;
> + unsigned int i;
> int ret = 0;
>
> mutex_lock(&pwm_lock);
>
> - pwm = _find_pwm(chip->pwm_id);
> - if (!pwm) {
> - ret = -ENOENT;
> - goto out;
> - }
> + for (i = chip->base; i < chip->base + chip->npwm; i++) {
> + struct pwm_desc *desc = pwm_to_desc(i);
>
> - if (test_bit(FLAG_REQUESTED, &pwm->flags)) {
> - ret = -EBUSY;
> - goto out;
> + if (test_bit(FLAG_REQUESTED, &desc->flags)) {
> + ret = -EBUSY;
> + goto out;
> + }
> }
>
> - list_del(&pwm->node);
> + free_descs(chip->base, chip->npwm);
> + of_pwmchip_remove(chip);
>
> - kfree(pwm);
> out:
> mutex_unlock(&pwm_lock);
> -
> return ret;
> }
> EXPORT_SYMBOL_GPL(pwmchip_remove);
>
> +/**
> + * pwmchip_find() - iterator for locating a specific pwm_chip
> + * @data: data to pass to match function
> + * @match: callback function to check pwm_chip
> + */
> +struct pwm_chip *pwmchip_find(void *data, int (*match)(struct pwm_chip *chip,
> + void *data))
> +{
> + struct pwm_chip *chip = NULL;
> + unsigned long i;
> +
> + mutex_lock(&pwm_lock);
> +
> + for_each_set_bit(i, allocated_pwms, MAX_PWMS) {
> + struct pwm_desc *desc = pwm_to_desc(i);
> +
> + if (!desc || !desc->chip)
> + continue;
> +
> + if (match(desc->chip, data)) {
> + chip = desc->chip;
> + break;
> + }
> + }
> +
> + mutex_unlock(&pwm_lock);
> +
> + return chip;
> +}
> +EXPORT_SYMBOL_GPL(pwmchip_find);
So, propreitary modules are not allowed to use PWMs?
> +
> /*
> * pwm_request - request a PWM device
> */
> -struct pwm_device *pwm_request(int pwm_id, const char *label)
> +struct pwm_device *pwm_request(int pwm, const char *label)
> {
> - struct pwm_device *pwm;
> + struct pwm_device *dev;
> + struct pwm_desc *desc;
> int ret;
>
> + if ((pwm < 0) || (pwm >= MAX_PWMS))
Don't need the inner parens.
> + return ERR_PTR(-ENOENT);
-EINVAL maybe?
> +
> mutex_lock(&pwm_lock);
>
> - pwm = _find_pwm(pwm_id);
> - if (!pwm) {
> - pwm = ERR_PTR(-ENOENT);
> - goto out;
> - }
> + desc = pwm_to_desc(pwm);
> + dev = &desc->pwm;
This looks wrong. If the pwm_desc being requested doesn't exist, won't
this oops?
>
> - if (test_bit(FLAG_REQUESTED, &pwm->flags)) {
> - pwm = ERR_PTR(-EBUSY);
> + if (test_bit(FLAG_REQUESTED, &desc->flags)) {
> + dev = ERR_PTR(-EBUSY);
> goto out;
> }
>
> - if (!try_module_get(pwm->chip->ops->owner)) {
> - pwm = ERR_PTR(-ENODEV);
> + if (!try_module_get(desc->chip->ops->owner)) {
> + dev = ERR_PTR(-ENODEV);
> goto out;
> }
>
> - if (pwm->chip->ops->request) {
> - ret = pwm->chip->ops->request(pwm->chip);
> + if (desc->chip->ops->request) {
> + ret = desc->chip->ops->request(desc->chip, pwm);
> if (ret) {
> - pwm = ERR_PTR(ret);
> + dev = ERR_PTR(ret);
> goto out_put;
> }
> }
>
> - pwm->label = label;
> - set_bit(FLAG_REQUESTED, &pwm->flags);
> + dev->label = label;
> + dev->pwm = pwm;
> + set_bit(FLAG_REQUESTED, &desc->flags);
>
> goto out;
>
> out_put:
> - module_put(pwm->chip->ops->owner);
> + module_put(desc->chip->ops->owner);
> out:
> mutex_unlock(&pwm_lock);
>
> - return pwm;
> + return dev;
> }
> EXPORT_SYMBOL_GPL(pwm_request);
>
> @@ -173,16 +311,19 @@ EXPORT_SYMBOL_GPL(pwm_request);
> */
> void pwm_free(struct pwm_device *pwm)
> {
> + struct pwm_desc *desc = container_of(pwm, struct pwm_desc, pwm);
> +
> mutex_lock(&pwm_lock);
pwm_lock is used to protect global addition and removal from the
radix/tree bitmap. Here you are also using it to protect the fields of a
specific pwm device? Maybe it would be better to have a per pwm device
lock for this?
> - if (!test_and_clear_bit(FLAG_REQUESTED, &pwm->flags)) {
> + if (!test_and_clear_bit(FLAG_REQUESTED, &desc->flags)) {
> pr_warning("PWM device already freed\n");
> goto out;
> }
>
> pwm->label = NULL;
> + pwm->pwm = 0;
Why do this? Isn't index 0 a valid PWM index?a
>
> - module_put(pwm->chip->ops->owner);
> + module_put(desc->chip->ops->owner);
> out:
> mutex_unlock(&pwm_lock);
> }
> @@ -193,7 +334,9 @@ EXPORT_SYMBOL_GPL(pwm_free);
> */
> int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
> {
> - return pwm->chip->ops->config(pwm->chip, duty_ns, period_ns);
> + struct pwm_desc *desc = container_of(pwm, struct pwm_desc, pwm);
> + return desc->chip->ops->config(desc->chip, pwm->pwm, duty_ns,
> + period_ns);
> }
> EXPORT_SYMBOL_GPL(pwm_config);
>
> @@ -202,8 +345,10 @@ EXPORT_SYMBOL_GPL(pwm_config);
> */
> int pwm_enable(struct pwm_device *pwm)
> {
> - if (!test_and_set_bit(FLAG_ENABLED, &pwm->flags))
> - return pwm->chip->ops->enable(pwm->chip);
> + struct pwm_desc *desc = container_of(pwm, struct pwm_desc, pwm);
> +
> + if (!test_and_set_bit(FLAG_ENABLED, &desc->flags))
> + return desc->chip->ops->enable(desc->chip, pwm->pwm);
>
> return 0;
> }
> @@ -214,7 +359,9 @@ EXPORT_SYMBOL_GPL(pwm_enable);
> */
> void pwm_disable(struct pwm_device *pwm)
> {
> - if (test_and_clear_bit(FLAG_ENABLED, &pwm->flags))
> - pwm->chip->ops->disable(pwm->chip);
> + struct pwm_desc *desc = container_of(pwm, struct pwm_desc, pwm);
> +
> + if (test_and_clear_bit(FLAG_ENABLED, &desc->flags))
> + desc->chip->ops->disable(desc->chip, pwm->pwm);
> }
> EXPORT_SYMBOL_GPL(pwm_disable);
> diff --git a/include/linux/pwm.h b/include/linux/pwm.h
> index df9681b..0f8d105 100644
> --- a/include/linux/pwm.h
> +++ b/include/linux/pwm.h
> @@ -32,37 +32,50 @@ void pwm_disable(struct pwm_device *pwm);
> struct pwm_chip;
>
> /**
> - * struct pwm_ops - PWM operations
> + * struct pwm_ops - PWM controller operations
> * @request: optional hook for requesting a PWM
> * @free: optional hook for freeing a PWM
> * @config: configure duty cycles and period length for this PWM
> * @enable: enable PWM output toggling
> * @disable: disable PWM output toggling
> + * @owner: helps prevent removal of modules exporting active PWMs
> */
> struct pwm_ops {
> - int (*request)(struct pwm_chip *chip);
> - void (*free)(struct pwm_chip *chip);
> - int (*config)(struct pwm_chip *chip, int duty_ns,
> + int (*request)(struct pwm_chip *chip,
> + unsigned int pwm);
> + void (*free)(struct pwm_chip *chip,
> + unsigned int pwm);
> + int (*config)(struct pwm_chip *chip,
> + unsigned int pwm, int duty_ns,
> int period_ns);
> - int (*enable)(struct pwm_chip *chip);
> - void (*disable)(struct pwm_chip *chip);
> + int (*enable)(struct pwm_chip *chip,
> + unsigned int pwm);
> + void (*disable)(struct pwm_chip *chip,
> + unsigned int pwm);
> struct module *owner;
> };
>
> /**
> - * struct pwm_chip - abstract a PWM
> - * @label: for diagnostics
> - * @owner: helps prevent removal of modules exporting active PWMs
> - * @ops: The callbacks for this PWM
> + * struct pwm_chip - abstract a PWM controller
> + * @dev: device providing the PWMs
> + * @ops: callbacks for this PWM controller
> + * @base: number of first PWM controlled by this chip
> + * @npwm: number of PWMs controlled by this chip
> */
> struct pwm_chip {
> - int pwm_id;
> - const char *label;
> + struct device *dev;
> struct pwm_ops *ops;
> + int base;
> + unsigned int npwm;
> };
>
> +int pwm_set_chip_data(unsigned int pwm, void *data);
> +void *pwm_get_chip_data(unsigned int pwm);
> +
> int pwmchip_add(struct pwm_chip *chip);
> int pwmchip_remove(struct pwm_chip *chip);
> +struct pwm_chip *pwmchip_find(void *data, int (*match)(struct pwm_chip *chip,
> + void *data));
> #endif
>
> #endif /* __LINUX_PWM_H */
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