help with coding a loadable kernel module

[Daniel Braniss]

> On Apr 17, 2015, at 4:42 PM, Warner Losh <imp at bsdimp.com> wrote:
> 
>> 
>> 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.
> 

I was afraid of that :-), this FDT stuff is new to me, and so far I was successful
in adding a gpio/led, but grep has not found any spibus.
any chance for a small template/example ? rpi or bbb would help!

cheers
	danny


>>> 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