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SubjectRe: [PATCH] leds: Add support for Philips PCA955x I2C LED drivers
On Wed, 14 May 2008 18:47:46 -0500
Nate Case <ncase@xes-inc.com> wrote:

> This driver supports the PCA9550, PCA9551, PCA9552, and PCA9553
> LED driver chips.
>
> ...
>
> +/* Set only the two bits in the LED selector register of the specified LED */
> +#define LED_SET(reg, led, state) \
> + ((reg & (~(0x3 << (led << 1)))) | ((state & 0x0F) << (led << 1)))

Please prefer to implement code in C rather than as a macro. Only use
macros when the code *must* be a macro.

For many reasons, one of which is: the above expression references
`led' twice and will misbehave if passed an expression which has
side-effects.

static inline void led_set(suitabletype reg, suitabletype led,
suitabletype state)

would suit.

(ditto NUM_INPUT_REGS, etc. Writing it in C will generate equivalent
code but we get a nicely lower-cased C function)

> +enum pca955x_type {
> + pca9550,
> + pca9551,
> + pca9552,
> + pca9553,
> +};
> +
> +struct pca955x_chipdef {
> + int bits;
> + u8 slv_addr; /* 7-bit slave address mask */
> + int slv_addr_shift; /* Number of bits to ignore */
> +};
> +
> +static struct pca955x_chipdef pca955x_chipdefs[] = {
> +[pca9550] = {
> + .bits = 2,
> + .slv_addr = /* 110000x */ 0x60,
> + .slv_addr_shift = 1,
> +},
> +[pca9551] = {
> + .bits = 8,
> + .slv_addr = /* 1100xxx */ 0x60,
> + .slv_addr_shift = 3,
> +},
> +[pca9552] = {
> + .bits = 16,
> + .slv_addr = /* 1100xxx */ 0x60,
> + .slv_addr_shift = 3,
> +},
> +[pca9553] = {
> + .bits = 4,
> + .slv_addr = /* 110001x */ 0x62,
> + .slv_addr_shift = 1,
> +},
> +};

the innards of the above should be tabbed one stop to the right.

> +static const struct i2c_device_id pca955x_id[] = {
> + { "pca9550", pca9550 },
> + { "pca9551", pca9551 },
> + { "pca9552", pca9552 },
> + { "pca9553", pca9553 },
> +};

oops, we forgot the terminating { } entry. It will crash...
> +MODULE_DEVICE_TABLE(i2c, pca955x_id);
>
> +struct pca955x_led {
> + struct pca955x_chipdef *chipdef;
> + struct i2c_client *client;
> + struct work_struct work;
> + spinlock_t lock;
> + enum led_brightness brightness;
> + struct led_classdev led_cdev;
> + int led_num; /* 0 .. 15 potentially */
> + char name[32];
> +};
> +
> +/*
> + * Write to frequency prescaler register, used to program the
> + * period of the PWM output. period = (PSCx + 1) / 38
> + */
> +static void pca955x_write_psc(struct i2c_client *client, int n, u8 val)
> +{
> + struct pca955x_led *pca955x = i2c_get_clientdata(client);

nanonit: most kernel code uses a single space between the type and the
identifier.

> +
> + i2c_smbus_write_byte_data(client,
> + NUM_INPUT_REGS(pca955x->chipdef->bits) + 2*n,
> + val);
> +}
>
> ...
>
> +void pca955x_led_set(struct led_classdev *led_cdev, enum led_brightness value)
> +{
> + struct pca955x_led *pca955x =
> + container_of(led_cdev, struct pca955x_led, led_cdev);

You're allowed to do

struct pca955x_led *pca955x;

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

;)

> + spin_lock(&(pca955x->lock));

unneeded parens

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

dittoes.

> +}
> +
> +static int __devinit pca955x_probe(struct i2c_client *client,
> + const struct i2c_device_id *id)
> +{
> + struct pca955x_led *pca955x;
> + int i;
> + int err = -ENODEV;
> + struct pca955x_chipdef *chip =
> + &pca955x_chipdefs[id->driver_data];
> + struct i2c_adapter *adapter =
> + to_i2c_adapter(client->dev.parent);
> + struct led_platform_data *pdata = client->dev.platform_data;
> +
> + DBG("probe() enter: chip 0x%02x, with type='%s'\n", client->addr,
> + id->name);
> +
> + /* Make sure the slave address / chip type combo given is possible */
> + if (((client->addr >> chip->slv_addr_shift) << chip->slv_addr_shift)
> + != chip->slv_addr) {

equivalent to the simpler

if (client->addr & ((1 << chip->slv_addr_shift) - 1)) {
I think?

> + dev_err(&client->dev, "invalid slave address %02x\n",
> + client->addr);
> + return -ENODEV;
> + }
> +
> + printk(KERN_INFO "leds-pca955x: Using %s %d-bit LED driver at "
> + "slave address 0x%02x\n",
> + id->name, chip->bits, client->addr);
> +
> + DBG("probe() checking i2c functionality\n");
> + if (!i2c_check_functionality(adapter, I2C_FUNC_I2C))
> + return -EIO;
> +
> + if (pdata) {
> + if (pdata->num_leds != chip->bits) {
> + dev_err(&client->dev, "board info claims %d LEDs"
> + " on a %d-bit chip\n",
> + pdata->num_leds, chip->bits);
> + return -ENODEV;
> + }
> + }
> +
> + for (i = 0; i < chip->bits; i++) {
> + pca955x = kzalloc(sizeof(struct pca955x_led), GFP_KERNEL);
> + if (!pca955x) {
> + err = -ENOMEM;
> + goto exit;
> + }
> +
> + pca955x->chipdef = chip;
> + pca955x->client = client;
> + pca955x->led_num = i;
> + /* Platform data can specify LED names and default triggers */
> + if (pdata) {
> + if (pdata->leds[i].name)
> + snprintf(pca955x->name, 32, "pca955x:%s",
> + pdata->leds[i].name);
> + if (pdata->leds[i].default_trigger)
> + pca955x->led_cdev.default_trigger =
> + pdata->leds[i].default_trigger;
> + } else {
> + snprintf(pca955x->name, 32, "pca955x:%d", i);
> + }
> + spin_lock_init(&pca955x->lock);
> +
> + pca955x->led_cdev.name = pca955x->name;
> + pca955x->led_cdev.brightness_set =
> + pca955x_led_set;
> +
> + /*
> + * Client data is a pointer to the _first_ pca955x_led
> + * struct
> + */
> + if (i == 0)
> + i2c_set_clientdata(client, pca955x);
> +
> + INIT_WORK(&(pca955x->work), pca955x_led_work);
> +
> + led_classdev_register(&client->dev, &(pca955x->led_cdev));
> + }
> +
> + /* Turn off LEDs */
> + for (i = 0; i < NUM_LED_REGS(chip->bits); i++)
> + pca955x_write_ls(client, i, 0x55);
> +
> + /* PWM0 is used for half brightness or 50% duty cycle */
> + pca955x_write_pwm(client, 0, 255-LED_HALF);
> +
> + /* PWM1 is used for variable brightness, default to OFF */
> + pca955x_write_pwm(client, 1, 0);
> +
> + /* Set to fast frequency so we do not see flashing */
> + pca955x_write_psc(client, 0, 0);
> + pca955x_write_psc(client, 1, 0);
> +
> + DBG("probe() returning\n");
> +
> + return 0;
> +exit:
> + return err;
> +}
> +


It's a neat-looking driver.


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