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    SubjectRe: [PATCH 1/1] iio: ak8975: Add Ak8975 magnetometer sensor
    On 09/03/10 06:18, samu.p.onkalo@nokia.com wrote:
    >
    >
    >> -----Original Message-----
    >> From: linux-iio-owner@vger.kernel.org [mailto:linux-iio-
    >> owner@vger.kernel.org] On Behalf Of ext Alan Cox
    >> Sent: 03 September, 2010 01:20
    >> To: achew@nvidia.com
    >> Cc: linux-kernel@vger.kernel.org; linux-iio@vger.kernel.org; linux-
    >> i2c@vger.kernel.org; akpm@linux-foundation.org; khali@linux-fr.org;
    >> ldewangan@nvidia.com
    >> Subject: Re: [PATCH 1/1] iio: ak8975: Add Ak8975 magnetometer sensor
    >>
    >>> +/*
    >>> + * Shows the device's mode. 0 = off, 1 = on.
    >>> + */
    >>
    >> Should this not be handled by runtime pm nowdays ?
    >>
    >>> + if ((oval < 0) || (oval > 1)) {
    >>> + dev_err(dev, "mode value is not supported\n");
    >>> + return -EINVAL;
    >>> + }
    >>
    >> ulong cannot be < 0 and doesn't need all the brackets
    >>
    >>
    >>> + /* Wait for the conversion to complete. */
    >>> + while (timeout_ms) {
    >>> + msleep(AK8975_CONVERSION_DONE_POLL_TIME);
    >>> + state = (gpio_get_value(data->eoc_gpio) ? 1 : 0);
    >>> + if (state)
    >>> + break;
    >>> + timeout_ms -= AK8975_CONVERSION_DONE_POLL_TIME;
    >>> + }
    >>
    >> This makes some fairly specific wiring assumptions about how the ak8975
    >> is configured. I'm looking at the ak8974 driver in our tree and also
    >> wondering if they can be combined sanely.
    >
    > With ak8974 chip, it is possible to have similar functionality without interrupt
    > pin. This is most probably true also for ak8975 chip. It is not good to assume
    > that everyone uses interrupt pin if the same functionally can be achieved
    > another way. I mean polling via I2C instead of checking GPIO state after the
    > sleep.
    Of course this can be done, but it's up to Andrew to decide whether he wants to.
    I think the usual principal of writing only what people currently need applies
    here. Perhaps a comment in the code to point out this could be done is a sensible
    compromise?
    >
    > Based on the this driver it seems that ak8974 and ak8975 are quite similar, but
    > also there are many differences like different register map. Maybe combining
    > these two makes implementation just messy.
    >
    >
    >>
    >>> + status = ak8975_read_data(client, AK8975_REG_ST1, 1,
    >> &read_status);
    >>> + if (!status) {
    >>> + dev_err(&client->dev, "Error in reading ST1\n");
    >>> + return false;
    >>
    >> I would have expected these to return a meaningful error code not 0 ?
    >>
    >>> +static IIO_DEVICE_ATTR(mode, S_IRUGO | S_IWUSR, show_mode,
    >> store_mode, 0);
    >>> +static IIO_DEVICE_ATTR(magn_x_calibscale, S_IRUGO, show_calibscale,
    >> NULL, 0);
    >>> +static IIO_DEVICE_ATTR(magn_y_calibscale, S_IRUGO, show_calibscale,
    >> NULL, 1);
    >>> +static IIO_DEVICE_ATTR(magn_z_calibscale, S_IRUGO, show_calibscale,
    >> NULL, 2);
    >>> +static IIO_DEV_ATTR_MAGN_X(show_raw, AK8975_REG_HXL);
    >>> +static IIO_DEV_ATTR_MAGN_Y(show_raw, AK8975_REG_HYL);
    >>> +static IIO_DEV_ATTR_MAGN_Z(show_raw, AK8975_REG_HZL);
    >>
    >> This seems odd as an interface as it's raw when the maths to provide
    >> non-raw (and thus abstract and easy for user space) data is trivial
    >> enough to do in kernel
    >>
    >> (but then I still suspect it should jusst be an input device of course)
    >>
    >>> +static int ak8975_probe(struct i2c_client *client,
    >>> + const struct i2c_device_id *id)
    >>> +{
    >>> + struct ak8975_data *data;
    >>> + int err;
    >>> +
    >>> + /* Allocate our device context. */
    >>> + data = kzalloc(sizeof(struct ak8975_data), GFP_KERNEL);
    >>> + if (!data) {
    >>> + dev_err(&client->dev, "Memory allocation fails\n");
    >>> + err = -ENOMEM;
    >>> + goto exit;
    >>> + }
    >>> +
    >>> + i2c_set_clientdata(client, data);
    >>> + data->client = client;
    >>> +
    >>> + mutex_init(&data->lock);
    >>> +
    >>> + /* Grab and set up the supplied GPIO. */
    >>> + data->eoc_irq = client->irq;
    >>> + data->eoc_gpio = irq_to_gpio(client->irq);
    >>
    >> It may not be via a GPIO. Better to do the GPIO handling in platform
    >> abstraction or accept passing IRQ and no GPIO value to mean "just use
    >> the
    >> IRQ". Ie do all the gpio foo if (data->eoc_gpio) { ... }
    >>
    >>
    >>> +
    >>> + err = gpio_request(data->eoc_gpio, "ak_8975");
    >>> + if (err < 0) {
    >>> + dev_err(&client->dev, "failed to request GPIO %d, error
    >> %d\n",
    >>> + data->eoc_gpio, err);
    >>> + goto exit_free;
    >>> + }
    >>> +
    >>> + err = gpio_direction_input(data->eoc_gpio);
    >>> + if (err < 0) {
    >>> + dev_err(&client->dev, "Failed to configure input direction
    >> for"
    >>> + " GPIO %d, error %d\n", data->eoc_gpio, err);
    >>> + gpio_free(data->eoc_gpio);
    >>
    >> This frees the GPIO twice ?
    >>
    >> Looks basically sound to me.
    >>
    >> Alan


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