Re: [PATCH] leds-pca955x: Fix race condition while setting brightness on several LEDs

From: Alexander Stein
Date: Tue Mar 20 2012 - 09:03:19 EST

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Any news/feedback on this?

Regards,
Alexander

Am Mittwoch, 8. Februar 2012, 13:44:08 schrieb Alexander Stein:
> 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 bewteen all LEDs.
>
> Signed-off-by: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxxxxxxxx>
> ---
> drivers/leds/leds-pca955x.c | 105
> ++++++++++++++++++++++++++----------------- 1 files changed, 64
> insertions(+), 41 deletions(-)
>
> diff --git a/drivers/leds/leds-pca955x.c b/drivers/leds/leds-pca955x.c
> index dcc3bc3..2980d8e 100644
> --- a/drivers/leds/leds-pca955x.c
> +++ b/drivers/leds/leds-pca955x.c
> @@ -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 */
> @@ -128,7 +133,7 @@ static inline int pca95xx_num_led_regs(int bits)
> * Return an LED selector register value based on an existing one, with
> * the appropriate 2-bit state value set for the given LED number (0-3).
> */
> -static inline u8 pca955x_ledsel(u8 oldval, int led_num, int state)
> +static inline u8 pca955x_ledel(u8 oldval, int led_num, int state)
> {
> return (oldval & (~(0x3 << (led_num << 1)))) |
> ((state & 0x3) << (led_num << 1));
> @@ -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,
> @@ -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,
> @@ -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,
> @@ -182,7 +187,7 @@ 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);
> @@ -190,26 +195,31 @@ static u8 pca955x_read_ls(struct i2c_client *client,
> int 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);
> + ls = pca955x_ledel(ls, ls_led, PCA955X_LS_LED_ON);
> break;
> case LED_OFF:
> - ls = pca955x_ledsel(ls, ls_led, PCA955X_LS_LED_OFF);
> + ls = pca955x_ledel(ls, ls_led, PCA955X_LS_LED_OFF);
> break;
> case LED_HALF:
> - ls = pca955x_ledsel(ls, ls_led, PCA955X_LS_BLINK0);
> + ls = pca955x_ledel(ls, ls_led, PCA955X_LS_BLINK0);
> break;
> default:
> /*
> @@ -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);
> - ls = pca955x_ledsel(ls, ls_led, PCA955X_LS_BLINK1);
> + pca955x_write_pwm(pca955x->client, 1,
> + 255 - pca955x_led->brightness);
> + ls = pca955x_ledel(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) @@ -233,7 +246,6 @@ 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;
>
> /*
> @@ -241,14 +253,13 @@ static void pca955x_led_set(struct led_classdev
> *led_cdev, enum led_brightness v * 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;
> @@ -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;
> }
> @@ -337,10 +357,12 @@ 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;
> @@ -348,14 +370,15 @@ exit:
>
> 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;
--
Dipl.-Inf. Alexander Stein

SYS TEC electronic GmbH
August-Bebel-Str. 29
D-07973 Greiz

Tel: +49-3661-6279-0, Fax: +49-3661-6279-99
eMail: Alexander.Stein@xxxxxxxxxxxxxxxxxxxxx
Internet: http://www.systec-electronic.com

Managing Director: Dipl.-Phys. Siegmar Schmidt
Commercial registry: Amtsgericht Jena, HRB 205563
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Next message: Ted Ts'o: "Re: [PATCH 2/9] ext4: Use pr_fmt and pr_<level>"
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