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RE: Problems when polling interrupt register



Bjorn is correct about the interrupt stuff, sorry for the
misleadning information.

If you need examples of blocking drivers you can look in
e.g. the ETRAX 100LX sync. serial driver (linux 2.4).

/Mikael

-----Original Message-----
From: Bjorn Wesen [mailto:bjornw@xxxxxxx.com]
Sent: Saturday, September 29, 2001 11:20 PM
To: Mikael Starvik
Cc: 'Jonsson, Marcus'; dev-etrax
Subject: RE: Problems when polling interrupt register


On Fri, 28 Sep 2001, Mikael Starvik wrote:
> >Do you think this is possible? If so, can I request the interrupt as
> >SA_INTERRUPT and avoid that the interrupt is interrupted?
> 
> SA_INTERRUPT means that the interrupt itself is not shared between
> different devices. It has nothing to do with if interrupts are enabled
> or not. Constructions like the following code can be used to make

Not true, SA_INTERRUPT means that the interrupt cannot be interrupted,
it's also known as a "fast interrupt". Sharing is controlled by
SA_SHIRQ, not allowed per default.

An interrupt registred with SA_INTERRUPT, never enables the interrupts
during execution of the handler.

> Also note that the normal interrupt handlers already has interrupts
> disabled while processing. If you need to do much stuff in the 
> interrupt handler you should register a bottom-half handler to
> avoid locking out the interrupts too much.

Not true - all 2.4 interrupts except the serial-port handlers are non
SA_INTERRUPT, meaning they are nested and can be interrupted by other
interrupts. 

Bottom-halves are deprecated in Linux 2.4, because they don't do anything
useful (since they still run in interrupt-context, just at another
time). Tasklets or kernel threads should be used for things that need to
run in non-interrupt context.

/Bjorn