help with coding a loadable kernel module

[Warner Losh]

> On Apr 17, 2015, at 7:26 AM, Daniel Braniss <danny at cs.huji.ac.il> wrote:
> 
>> 
>> On Apr 17, 2015, at 4:13 PM, Ian Lepore <ian at freebsd.org> wrote:
>> 
>> On Fri, 2015-04-17 at 13:46 +0300, Daniel Braniss wrote:
>>>> On Apr 17, 2015, at 12:55 PM, Tom Jones <jones at sdf.org> wrote:
>>>> 
>>>> On Fri, Apr 17, 2015 at 12:15:33PM +0300, Daniel Braniss wrote:
>>>>> 
>>>>>> On Apr 17, 2015, at 11:08 AM, Kurt Jaeger <lists at opsec.eu> wrote:
>>>>>> 
>>>>>> Hi!
>>>>>> 
>>>>>>> I know I'm embarking on a dangerous trip, but I want to use a Raspberry Pi
>>>>>>> and or a BeagleBone to read (and write) RFID cards.
>>>>>>> Since a driver is needed to use the spibus, I have 2 options while
>>>>>>> developing:
>>>>>> [...]
>>>>>>> So before I give up on option 2, is there some examples/help?
>>>>>> 
>>>>>> Are you aware of this book ?
>>>>>> 
>>>>>> http://www.nostarch.com/bsddrivers.htm <http://www.nostarch.com/bsddrivers.htm>
>>>>> 
>>>>> no, but before I spend more money (this is getting expensive :-),
>>>>> does it explain how to write a loadable module that needs to to talk
>>>>> to a spibus?
>>>> 
>>>> I don't think it does.
>>>> 
>>>> spibus is very simple, there is one interface call
>>>> 
>>>> SPIBUS_TRANSFER(device_t, device_t, strcut spi_command);
>>>> 
>>> 
>>> chicken and egg issue :-), what device_t dev should I use?
>>> it must point to the spibus …
>> 
>> Your device will be a child of the spibus, and it is the bus that
> 
> it’s the ‘child of’ that I have problems. this will be a loadable module, so
> it will have to tell the parent that he is no longer an orphan :-)

When you declare the module, one of the parameters are what bus to
attach to.

If you are using FDT in your system, then you’ll put your device into the
FDT tree below the spibus to create the device_t node in the tree. When
your module is loaded, its probe routine will be called, and you can
match based on the compatible string given in the FDT.

>> implements the SPIBUS_TRANSFER() method, so it's the bus's device_t that
>> needs to be passed as the first parameter in the call (if it were C++ it
>> would be the "this" pointer -- this stuff is OO implemented in plain-C).
>>> From your driver, something like:
>> 
>> SPIBUS_TRANSFER(device_get_parent(sc->sc_dev), sc->sc_dev, cmdptr);
>> 
>> I haven't got time this morning to put together a complete example of
>> how to add a module to the build, but the process is basically along the
>> lines of...
>> 
>> Add a new directory to sys/dev for your driver just like you were
>> going to compile it into the kernel.  Then in sys/modules find another
>> simple driver, copy it to a new directory, and change the names of
>> things in the makefile so that it refers to your new dir/files in
>> sys/dev.  You can set MODULES_OVERRIDE=yournew_dirname on the make
>> command line or in your kernel config to make it compile.
>> 
> 
> I have that, even figured out how to cross compile and use the make buildenv.
> it’s great! I can compile outside the source tree too.

Yes. That’s also possible. Build it in a buildenv environment and then
copy the .ko file over to the target system to kldload.

Warner

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