linux-kernel - Re: musb as module broken in 2.6.38

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Date:	Wed, 16 Mar 2011 12:48:03 +0200
From:	Felipe Balbi <balbi@...com>
To:	Alexander Holler <holler@...oftware.de>
Cc:	Felipe Balbi <balbi@...com>, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: musb as module broken in 2.6.38

Hi,

On Mar 16, 2011, at 12:43 PM, Alexander Holler wrote:

> Am 16.03.2011 11:38, schrieb Felipe Balbi:
>> hi,
>> 
>> On Mar 16, 2011, at 12:30 PM, Alexander Holler wrote:
>>> Am 16.03.2011 11:24, schrieb Felipe Balbi:
>>>> Hi,
>>>> 
>>>> On Mar 16, 2011, at 12:17 PM, Alexander Holler wrote:
>>>>>> static int __init omap2430_probe(struct platform_device *pdev)
>>>>> 
>>>>> Neither omap2430_init() nor omap2430_probe() will be called here.
>>>> 
>>>> and why is that ? It's even in sysfs already:
>>>> 
>>>>>>> beagle linux # ls /sys/devices/platform/ | grep musb
>>>>>>> musb-omap2430
>>> 
>>> Don't know, I haven't written or changed the driver. ;)
>> 
>> hehe, Just thought that you had something in mind already.
>> 
>> probe() functions are called when, in case of platform_devices,
>> the name matches with driver name. musb-omap2430 platform_device
>> is allocated in arch/arm/mach-omap2/usb-musb.c, then musb-2430
>> driver lives in drivers/usb/musb/omap2430.c. musb-2430 allocates a
>> platform_device for musb-hdrc core driver.
>> 
>> We did that because the same core is used in many different platforms
>> (OMAP, discrete chips, ST-Ericsson, DaVinci, PCI cards, etc) so we
>> needed to "abstract" platform-specific details such as clock handling
>> and power management.
>> 
>> There's still work to be done, for sure, e.g. the DMA part is still quite
>> screwed up, but the drivers are correctly named which means they
>> should be matching and probing. Now, musb-hdrc isn't probing, as
>> you say, and I'd like to know why. I'll try to spend some time in
>> it when I get back to the office.
> 
> I currently assume it's something with
> 
> subsys_initcall(omap2430_init);
> 
> Have to read about subsys_initcall() and why omap2430_init isn't called here.

I guess I know what the problem is. If you search for omap2430_init
in vmlinux it won't be there. I guess when a directory is marked as 
obj-m, Kbuild won't search for symbols to be statically linked to vmlinux
on that directory. Since we use the same Kconfig entry to select musb as
module and include drivers/usb/musb directory into build system, we
are falling into that case.

Try changing drivers/usb/musb to obj-y in drivers/Makefile and see if things
start working.

-- 
balbi

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