How to use spi device from another kernel module?

[Ran Shalit]

On Wed, Dec 7, 2016 at 8:21 PM, Ran Shalit <ranshalit at gmail.com> wrote:
> 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. :)
>>>
If I may please ask one more thing on this issue, just for my understanding.
Before trying the above suggestions, I made the following trial (which
I know is quick and dirty ):

I copied the pointer to spi device from probe() function into static
variable and than tried to use it later (in proc/sysfs), but I get
exceptions.
I am not going to use this method anyway, yet I am curious why it doesn't work.

Thank you,
Ran

>>
>> 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