How to use spi device from another kernel module?

[Ran Shalit]

On Wed, Dec 7, 2016 at 7:26 PM, Ran Shalit <ranshalit at gmail.com> wrote:
> On Wed, Dec 7, 2016 at 6:58 PM, Joel Fernandes <agnel.joel at gmail.com> wrote:
>> On Tue, Dec 6, 2016 at 11:02 PM, Greg KH <greg at kroah.com> wrote:
>>> On Tue, Dec 06, 2016 at 09:12:24PM -0800, Joel Fernandes wrote:
>>>> On Tue, Dec 6, 2016 at 11:42 AM, Ran Shalit <ranshalit at gmail.com> wrote:
>>>> > Hello,
>>>> >
>>>> > I have spi device which is registered using spi_register_board_info(),
>>>> > and I would like to get a pointer to this device in some other kernel module.
>>>> >
>>>> > Is there a simple way to get a pointer to pointer to a device , so
>>>> > that we can use it from other module ? (something like i2c_get_adapter
>>>> > for i2c)
>>>>
>>>> Find out what's the SPI bus number (for the master) and the chip
>>>> select on that SPI master (for the SPI device)
>>>>
>>>> Then you can use bus_for_each_device on spi_bus_type and find the
>>>> spi_device you're looking for. See the following code for an example
>>>> of how to use bus_for_each_device:

Hi,

I did try using this method with the following call:

bus_for_each_dev(&spi_bus_type, NULL, NULL, spi_device_found);

static int spi_device_found(struct device *dev, void *data)
{
    struct spi_device *spi = container_of(dev, struct spi_device, dev);

    printk(":      %s %s %dkHz %d bits mode=0x%02X\n",
        spi->modalias, dev_name(dev), spi->max_speed_hz/1000,
        spi->bits_per_word, spi->mode);

    return 0;
}

But for some reason the list is empty, although I do have devices
registered successfuly with spi_register_driver.
Using the same method with i2c works well, not sure why it doesn't
list anything with spi.

Thanks,
Ran

>>>>
>>>> http://lxr.free-electrons.com/source/drivers/spi/spi.c#L524
>>>>
>>>> In your check function, just make sure your spi->master->bus_num is
>>>> the bus you want and the spi->chip_select is the chip select
>>>> corresponding to the device you want. If both these conditions are
>>>> satisfied, there you have your spi_device.
>>>
>>> Eeek, no, please never do that, use the proper spi apis to get your
>>> needed device.  They are there somewhere, using a "raw"
>>> bus_for_each_device is never the answer unless you are a bus and
>>> iterating over your own device list.
>>
>> Yes I completely agree, maybe I assumed too much and thought he was
>> trying to do this for some quick debugging from some kernel module,
>> and was just looking for a quick and dirty way to get to a spi_device.
>> Was not really suggesting this for production code. :)
>>
>
> You were actually Right... That's exactly what I wanted :) , so I
> probably will  try to use your simple method.
> I think that for production , spidev shows a good example how to use
> spi as a char device:
> https://github.com/Xilinx/linux-xlnx/blob/master/drivers/spi/spidev.c
>
> Thanks!
> Ran
>
>> Regards,
>> Joel
>>
>>>
>>> thanks,
>>>
>>> greg k-h