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    SubjectRe: [PATCH 1/3] drivers: misc: ak8974 / ami305 magnetometer driver
    > +static int ak8974_regulators_on(struct ak8974_chip *chip)
    > +{
    > + int ret;
    > + ret = regulator_bulk_enable(ARRAY_SIZE(chip->regs), chip->regs);
    > + if (ret == 0)
    > + msleep(AK8974_POWERON_DELAY);
    > +
    > + return ret;
    > +}
    > +
    > +static inline void ak8974_regulators_off(struct ak8974_chip *chip)
    > +{
    > + regulator_bulk_disable(ARRAY_SIZE(chip->regs), chip->regs);
    > +}

    That bit seems platform specific but in generic code ?


    > +static ssize_t ak8974_misc_read(struct file *file, char __user *buf,
    > + size_t count, loff_t *offset)
    > +{
    > + struct ak8974_chip *chip = container_of(file->private_data,
    > + struct ak8974_chip,
    > + miscdev);
    > + struct ak8974_data data;

    So we have a different API to the ak8975 just posted and to the other
    existing devices. This needs sorting out across the devices before there
    is a complete disaster. Right now we have a mix of submissions pending
    which variously use

    misc + sysfs
    sysfs
    input (reporting X Y Z etc axes)

    Someone needs to decide on a single API before it's too late.

    > +
    > + if (count < sizeof(data))
    > + return -EINVAL;
    > +
    > + if (*offset >= chip->offset) {
    > + schedule_work(&chip->work);
    > + if (file->f_flags & O_NONBLOCK)
    > + return -EAGAIN;
    > + if (wait_event_interruptible(chip->misc_wait,
    > + (*offset < chip->offset)))
    > + return -ERESTARTSYS;
    > + }
    > +
    > + mutex_lock(&chip->lock);
    > + data.x = chip->x;
    > + data.y = chip->y;
    > + data.z = chip->z;
    > + data.valid = chip->valid;
    > + *offset = chip->offset;
    > + mutex_unlock(&chip->lock);

    What happens if you have two readers - is it fine they get copies of the
    same event when it races ?


    > +
    > + return copy_to_user(buf, &data, sizeof(data)) ? -EFAULT : sizeof(data);

    Pedantically if data is consumed and a partial copy occurs you should
    return the bytes successfully copied.

    > +static DEVICE_ATTR(chip_id, S_IRUGO, ak8974_show_chip_id, NULL);
    > +
    > +static ssize_t ak8974_show_range(struct device *dev,
    > + struct device_attribute *attr, char *buf)
    > +{
    > + struct ak8974_chip *chip = dev_get_drvdata(dev);
    > + return sprintf(buf, "%d\n", chip->max_range);
    > +}

    Other devices make all of this sysfs or use input. We need to work out
    what the right interface actually is.

    > + snprintf(chip->name, sizeof(chip->name), "ak8974%d",
    > + atomic_add_return(1, &device_number) - 1);

    Surely this is serialized anyway ?


    > +#ifdef CONFIG_PM
    > +static int ak8974_suspend(struct i2c_client *client, pm_message_t mesg)
    > +{
    > + struct ak8974_chip *chip = i2c_get_clientdata(client);
    > + mutex_lock(&chip->users_lock);
    > + if (chip->users > 0)
    > + ak8974_enable(chip, AK8974_PWR_OFF);
    > + mutex_unlock(&chip->users_lock);
    > + return 0;
    > +}
    > +
    > +static int ak8974_resume(struct i2c_client *client)
    > +{
    > + struct ak8974_chip *chip = i2c_get_clientdata(client);
    > + mutex_lock(&chip->users_lock);
    > + if (chip->users > 0)
    > + ak8974_enable(chip, AK8974_PWR_ON);
    > + mutex_unlock(&chip->users_lock);
    > + return 0;
    > +}

    The whole chip->users thing you are implementing is basically a
    reimplementation of the kernel runtime pm stuff - so can that be used
    instead ?


    > +#ifndef __LINUX_I2C_AK8974_H
    > +#define __LINUX_I2C_AK8974_H
    > +
    > +#define AK8974_NO_MAP 0
    > +#define AK8974_DEV_X 1
    > +#define AK8974_DEV_Y 2
    > +#define AK8974_DEV_Z 3
    > +#define AK8974_INV_DEV_X -1
    > +#define AK8974_INV_DEV_Y -2
    > +#define AK8974_INV_DEV_Z -3
    > +
    > +struct ak8974_platform_data {
    > + s8 axis_x;
    > + s8 axis_y;
    > + s8 axis_z;
    > +};
    > +
    > +/* Device name: /dev/ak8974n, where n is a running number */
    > +struct ak8974_data {
    > + __s16 x;
    > + __s16 y;
    > + __s16 z;
    > + __u16 valid;
    > +} __attribute__((packed));

    This could go in the C file.


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