Re: [Xenomai-help] RTDM and spi

[Philippe Gerum <rpm@xenomai.org>]

On 01/05/2012 11:28 PM, Terry Fryar wrote:
> Ah...simple enough!  One question though...are the xenomai sync services
> items and irq functions available for non-RT kernel threads??

IRQ related routines? like request, enable, disable: yes. It's even 
recommended to use them in that context actually.

Xenomai blocking services can only be used over a Xenomai thread, that 
is a golden rule. Reason: to wait for a sync, the thread has to be held 
by the scheduler of the kernel in question while it sleeps. Only Xenomai 
threads have the required internal data to allow the Xenomai scheduler 
to hold them.

>
> -----Original Message-----
> From: Philippe Gerum [mailto:rpm@xenomai.org]
> Sent: Thursday, January 05, 2012 4:25 PM
> To: Terry Fryar
> Cc: xenomai@xenomai.org
> Subject: Re: [Xenomai-help] RTDM and spi
>
> On 01/05/2012 11:12 PM, Terry Fryar wrote:
>> Using the RTDM api with Xen 2.6 to develop a linux driver.
>> Basically have an ISR registered using *rtdm_irq_request*()that is
>> triggered from a gpio pin. ISR works fine. Inside ISR, the only thing
>> done is a *rtdm_event_signal*() on an event.
>> Then, I have a task created using *rtdm_task_init*() that is waiting
>> on the event using *rtdm_event_timedwait*().
>> So far, so good...all works. But, in the task I am making an SPI call
>> after the event is signaled using spi_message_add_tail() and
>> spi_sync() and that's where I get this:
>> BUG: sleeping function called from invalid context at
>> kernel/mutex.c:278 [ 98.449178] in_atomic(): 1, irqs_disabled(): 0, pid:
> -555875760, name:
>> vÿÿýÿ¿·½ÿ§ÿÿõ>ÿÿýw¿@ÞÞPÞÞ
>> [ 98.458686] INFO: lockdep is turned off.
>> [ 98.462811] [<c00572ac>] (unwind_backtrace+0x0/0xe0) from
>> [<c04639bc>]
>> (mutex_lock_nested+0x24/0x384)
>> [ 98.472501] [<c04639bc>] (mutex_lock_nested+0x24/0x384) from
>> [<c033ca48>] (__spi_sync+0x88/0xd8) [ 98.481730] [<c033ca48>]
>> (__spi_sync+0x88/0xd8) from [<bf007180>]
>> (irqdrv_task+0x44/0xd4 [irqdrv])
>> [ 98.491149] [<bf007180>] (irqdrv_task+0x44/0xd4 [irqdrv]) from
>> [<c00e93d0>] (xnarch_thread_trampoline+0x20/0x2c)
>> [ 98.501845] [<c00e93d0>] (xnarch_thread_trampoline+0x20/0x2c) from
>> [<c00e5adc>] (__xnpod_schedule+0x5cc/0xa54) [ 98.512355] [<c00e5adc>]
>> (__xnpod_schedule+0x5cc/0xa54) from [<fff7febf>] (0xfff7febf) [
>> 98.520674] Xenomai: suspending kernel thread bf008180 ('irqdrvTask')
>> at 0xc00a92f8 after exception #0x0 I have tried this inside a kthread
>> and it works fine. I can also try the spi stuff without being
>> triggered by an IRQ, and I get the same error. I know this is
>> something simple???
>
> You may not call the regular Linux kernel routines from a real-time context.
> You have two kernels running side by side, Linux and Xenomai,
> unsynchronized. Your RTDM driver is entering __spi_sync() over a non-Linux
> context, this can't work since that context may have preempted Linux
> anywhere, including in the middle of what Linux thinks is an atomic section.
>
> Any kernel code you want to call from the real-time co-kernel has to be
> adapted to support this. Specifically, you cannot run the regular SPI stack
> over a real-time RTDM context.
>
>>
>>
>>
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>> Xenomai-help@domain.hid
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>
>


-- 
Philippe.