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drivers/leds/leds-pca955x.c: fix race condition while setting brightn…
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…ess on several LEDs

When issuing the following command:

  for I in 0 1 2 3 4 5 6 7; do
    echo 0 > /sys/class/leds/pca955x\:${I}/brightness;
  done

It is possible that all the pca955x_read_ls calls are done sequentially
before any pca955x_write_ls call is done.  This updates the LS only to
the last LED update in its set.

Fix this by using a global lock for the pca995x device during
pca955x_led_work.  Also used a struct for shared data betreen all LEDs.

[akpm@linux-foundation.org: revert unintentional rename of pca955x_ledsel()]
Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Bryan Wu <bryan.wu@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@torvalds
Alexander Stein authored and torvalds committed May 29, 2012
1 parent 44e1e9f commit e7e11d8
Showing 1 changed file with 59 additions and 36 deletions.
95 changes: 59 additions & 36 deletions drivers/leds/leds-pca955x.c
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Original file line number Diff line number Diff line change
Expand Up @@ -101,11 +101,16 @@ static const struct i2c_device_id pca955x_id[] = {
};
MODULE_DEVICE_TABLE(i2c, pca955x_id);

struct pca955x_led {
struct pca955x {
struct mutex lock;
struct pca955x_led *leds;
struct pca955x_chipdef *chipdef;
struct i2c_client *client;
};

struct pca955x_led {
struct pca955x *pca955x;
struct work_struct work;
spinlock_t lock;
enum led_brightness brightness;
struct led_classdev led_cdev;
int led_num; /* 0 .. 15 potentially */
Expand Down Expand Up @@ -140,7 +145,7 @@ static inline u8 pca955x_ledsel(u8 oldval, int led_num, int state)
*/
static void pca955x_write_psc(struct i2c_client *client, int n, u8 val)
{
struct pca955x_led *pca955x = i2c_get_clientdata(client);
struct pca955x *pca955x = i2c_get_clientdata(client);

i2c_smbus_write_byte_data(client,
pca95xx_num_input_regs(pca955x->chipdef->bits) + 2*n,
Expand All @@ -156,7 +161,7 @@ static void pca955x_write_psc(struct i2c_client *client, int n, u8 val)
*/
static void pca955x_write_pwm(struct i2c_client *client, int n, u8 val)
{
struct pca955x_led *pca955x = i2c_get_clientdata(client);
struct pca955x *pca955x = i2c_get_clientdata(client);

i2c_smbus_write_byte_data(client,
pca95xx_num_input_regs(pca955x->chipdef->bits) + 1 + 2*n,
Expand All @@ -169,7 +174,7 @@ static void pca955x_write_pwm(struct i2c_client *client, int n, u8 val)
*/
static void pca955x_write_ls(struct i2c_client *client, int n, u8 val)
{
struct pca955x_led *pca955x = i2c_get_clientdata(client);
struct pca955x *pca955x = i2c_get_clientdata(client);

i2c_smbus_write_byte_data(client,
pca95xx_num_input_regs(pca955x->chipdef->bits) + 4 + n,
Expand All @@ -182,26 +187,31 @@ static void pca955x_write_ls(struct i2c_client *client, int n, u8 val)
*/
static u8 pca955x_read_ls(struct i2c_client *client, int n)
{
struct pca955x_led *pca955x = i2c_get_clientdata(client);
struct pca955x *pca955x = i2c_get_clientdata(client);

return (u8) i2c_smbus_read_byte_data(client,
pca95xx_num_input_regs(pca955x->chipdef->bits) + 4 + n);
}

static void pca955x_led_work(struct work_struct *work)
{
struct pca955x_led *pca955x;
struct pca955x_led *pca955x_led;
struct pca955x *pca955x;
u8 ls;
int chip_ls; /* which LSx to use (0-3 potentially) */
int ls_led; /* which set of bits within LSx to use (0-3) */

pca955x = container_of(work, struct pca955x_led, work);
chip_ls = pca955x->led_num / 4;
ls_led = pca955x->led_num % 4;
pca955x_led = container_of(work, struct pca955x_led, work);
pca955x = pca955x_led->pca955x;

chip_ls = pca955x_led->led_num / 4;
ls_led = pca955x_led->led_num % 4;

mutex_lock(&pca955x->lock);

ls = pca955x_read_ls(pca955x->client, chip_ls);

switch (pca955x->brightness) {
switch (pca955x_led->brightness) {
case LED_FULL:
ls = pca955x_ledsel(ls, ls_led, PCA955X_LS_LED_ON);
break;
Expand All @@ -219,12 +229,15 @@ static void pca955x_led_work(struct work_struct *work)
* OFF, HALF, or FULL. But, this is probably better than
* just turning off for all other values.
*/
pca955x_write_pwm(pca955x->client, 1, 255-pca955x->brightness);
pca955x_write_pwm(pca955x->client, 1,
255 - pca955x_led->brightness);
ls = pca955x_ledsel(ls, ls_led, PCA955X_LS_BLINK1);
break;
}

pca955x_write_ls(pca955x->client, chip_ls, ls);

mutex_unlock(&pca955x->lock);
}

static void pca955x_led_set(struct led_classdev *led_cdev, enum led_brightness value)
Expand All @@ -233,22 +246,20 @@ static void pca955x_led_set(struct led_classdev *led_cdev, enum led_brightness v

pca955x = container_of(led_cdev, struct pca955x_led, led_cdev);

spin_lock(&pca955x->lock);
pca955x->brightness = value;

/*
* Must use workqueue for the actual I/O since I2C operations
* can sleep.
*/
schedule_work(&pca955x->work);

spin_unlock(&pca955x->lock);
}

static int __devinit pca955x_probe(struct i2c_client *client,
const struct i2c_device_id *id)
{
struct pca955x_led *pca955x;
struct pca955x *pca955x;
struct pca955x_led *pca955x_led;
struct pca955x_chipdef *chip;
struct i2c_adapter *adapter;
struct led_platform_data *pdata;
Expand Down Expand Up @@ -282,39 +293,48 @@ static int __devinit pca955x_probe(struct i2c_client *client,
}
}

pca955x = kzalloc(sizeof(*pca955x) * chip->bits, GFP_KERNEL);
pca955x = kzalloc(sizeof(*pca955x), GFP_KERNEL);
if (!pca955x)
return -ENOMEM;

pca955x->leds = kzalloc(sizeof(*pca955x_led) * chip->bits, GFP_KERNEL);
if (!pca955x->leds) {
err = -ENOMEM;
goto exit_nomem;
}

i2c_set_clientdata(client, pca955x);

mutex_init(&pca955x->lock);
pca955x->client = client;
pca955x->chipdef = chip;

for (i = 0; i < chip->bits; i++) {
pca955x[i].chipdef = chip;
pca955x[i].client = client;
pca955x[i].led_num = i;
pca955x_led = &pca955x->leds[i];
pca955x_led->led_num = i;
pca955x_led->pca955x = pca955x;

/* Platform data can specify LED names and default triggers */
if (pdata) {
if (pdata->leds[i].name)
snprintf(pca955x[i].name,
sizeof(pca955x[i].name), "pca955x:%s",
pdata->leds[i].name);
snprintf(pca955x_led->name,
sizeof(pca955x_led->name), "pca955x:%s",
pdata->leds[i].name);
if (pdata->leds[i].default_trigger)
pca955x[i].led_cdev.default_trigger =
pca955x_led->led_cdev.default_trigger =
pdata->leds[i].default_trigger;
} else {
snprintf(pca955x[i].name, sizeof(pca955x[i].name),
snprintf(pca955x_led->name, sizeof(pca955x_led->name),
"pca955x:%d", i);
}

spin_lock_init(&pca955x[i].lock);

pca955x[i].led_cdev.name = pca955x[i].name;
pca955x[i].led_cdev.brightness_set = pca955x_led_set;
pca955x_led->led_cdev.name = pca955x_led->name;
pca955x_led->led_cdev.brightness_set = pca955x_led_set;

INIT_WORK(&pca955x[i].work, pca955x_led_work);
INIT_WORK(&pca955x_led->work, pca955x_led_work);

err = led_classdev_register(&client->dev, &pca955x[i].led_cdev);
err = led_classdev_register(&client->dev,
&pca955x_led->led_cdev);
if (err < 0)
goto exit;
}
Expand All @@ -337,25 +357,28 @@ static int __devinit pca955x_probe(struct i2c_client *client,

exit:
while (i--) {
led_classdev_unregister(&pca955x[i].led_cdev);
cancel_work_sync(&pca955x[i].work);
led_classdev_unregister(&pca955x->leds[i].led_cdev);
cancel_work_sync(&pca955x->leds[i].work);
}

kfree(pca955x->leds);
exit_nomem:
kfree(pca955x);

return err;
}

static int __devexit pca955x_remove(struct i2c_client *client)
{
struct pca955x_led *pca955x = i2c_get_clientdata(client);
struct pca955x *pca955x = i2c_get_clientdata(client);
int i;

for (i = 0; i < pca955x->chipdef->bits; i++) {
led_classdev_unregister(&pca955x[i].led_cdev);
cancel_work_sync(&pca955x[i].work);
led_classdev_unregister(&pca955x->leds[i].led_cdev);
cancel_work_sync(&pca955x->leds[i].work);
}

kfree(pca955x->leds);
kfree(pca955x);

return 0;
Expand Down

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