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    Subjectdevice driver probe return codes
    I would like some feedback on the following regarding some
    form of standardising return codes from a device driver probe
    to try and stop some basic mistakes.

    This document is not complete, any additions would be welcone.

    probe() error return codes

    -ENODEV This should be reserved for the case where there
    really is no device here.

    If you do not have a necessary resource or other setup
    information this is NOT the error you want to return as
    the driver core will not print any error message to the
    user. Even if you driver prints a warning, this is still
    not the error code to return.

    -ENXIO See -ENODEV, this is taken by the driver core to mean
    there is "No such device or address (POSIX.1)".

    -ENOMEM This is used to signify lack of memory resources, such
    as a failure to kmalloc() device state.

    -EBUSY A resource you need is not avaialable.

    This is returned if you cannot get exclusive access to a
    resource such as a request_mem_region() has failed.

    -EINVAL An argument to the driver is invalid.

    -EIO An input/output error occured. This could be due to
    the device responding in an unexpected way or that
    the device did not complete a request properly.

    Generic driver examples

    Requesting an memory region

    if (!request_mem_region(start, len, why))
    return -EBUSY;

    Mapping a IO region

    regs = ioremap(base, size);
    if (!regs)
    return -EIO;

    possibly -EFAULT here?

    Not -ENOMEM, which a number of drivers do.

    Platform driver specific examples

    Examples when writing platform drivers.

    All examples in this section assume the probe prototype is:

    static int my_probe(struct platform_device *pdev)

    Checking platform data

    if (!pdev->dev.platform_data)
    return -EINVAL;

    should -ENOENT be returned here?

    Finding platform resource(s)

    res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    if (!res)
    return -ENOENT;

    Getting a clock

    clk = clk_get(&pdev->dev, NULL);
    if (IS_ERR(clk))
    return PTR_ERR(clk);

    Ben (,

    'a smiley only costs 4 bytes'

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