405 Critical Interrupts

405 Critical Interrupts

[Felix Domke]

Hi,

i need to have a low-latency interrupt on a 405-based chip with linux 2.4.

Did anybody yet worked on this?

I thought about routing the CriticalInterrupt pretty much the same way
as the HardwareInterrupt, but with disabling MSR_CE. MSR_CE would be
enabled then even in (normal) interrupts, we probably have to add a
__crit_cli and __save_and_crit_cli as someone already suggested.

Does CRIT_EXCEPTION work? Is do_IRQ reentrant? Should i use the same
interrupt processing as a normal hardware interrupt, with the exception
that only "critical"-flagged interrupts are processed?

Any suggestions?

The background: the IBM-STB045xx's capture port, which we use for
IR-decoding, doesn't have any buffering, so when a time-consuming
interrupt is processed (PIO network, maybe PIO ide), we miss IR cycles.

Felix


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Re: 405 Critical Interrupts

[Matt Porter]

On Wed, Nov 26, 2003 at 05:28:37PM +0100, Felix Domke wrote:
> I thought about routing the CriticalInterrupt pretty much the same way
> as the HardwareInterrupt, but with disabling MSR_CE. MSR_CE would be
> enabled then even in (normal) interrupts, we probably have to add a
> __crit_cli and __save_and_crit_cli as someone already suggested.
>
> Does CRIT_EXCEPTION work? Is do_IRQ reentrant? Should i use the same
> interrupt processing as a normal hardware interrupt, with the exception
> that only "critical"-flagged interrupts are processed?
>
> Any suggestions?

You could backport the critical exception handling code from 2.6.

-Matt

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Re: 405 Critical Interrupts

[Takeharu KATO]

Dear Domke :

>>Does CRIT_EXCEPTION work? Is do_IRQ reentrant? Should i use the same
>>interrupt processing as a normal hardware interrupt, with the exception
>>that only "critical"-flagged interrupts are processed?
>>
>>Any suggestions?
>>
>>
As far as I know, critical interrupt in ppc4xx archetecture is handled
as  a kind of unknown Interrupts. So It make system down in 2.6 series
(this may also be true in 2.4).

In linux kernel , the kernel stack is changed to critical interrupt
stack instead of
user process's kernel stack when it occuers in super visor mode.
So do_IRQ can not be called in crittical interrupt(because it call
preempt relevant
functions).

We have  implemeted critical interrupt handling facilites in 2.6 kernel .
In this implementation, critical interrupt specific interrupt handling
routines.
If you need our patch, please contact me(cause we need some periods to
prepare the patch).

Regards,

--
Takeharu KATO
Fujitsu Limited
Email:tkato@cs.fujitsu.co.jp (ext. 7112-4621)


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