Anders Blomdell wrote:
Jan Kiszka wrote:

Philippe Gerum wrote:

Jan Kiszka wrote:

Dmitry Adamushko wrote:


...
This said, I'm going to publish the shirq patch (after finalizing ISR
return
bits,
where I still have some doubts) without enable/disable nesting support. It can be supported at some point of time later, if it's really needed.



Regarding enable/disable nesting and existing driver patterns: I
currently do the following on devices init via RTDM (and users may have
copied this):

rtdm_irq_request(...);
<init_hardware, also clear pending IRQs of the device>
rtdm_irq_enable(...);

But I do not disable the IRQ before rtdm_irq_free() again. Is this
unbalanced enabling still needed today? Is it even wrong these days?


Looks unsafe, since nothing says that freeing the descriptor associated
with some IRQ should disable this IRQ line at hw level. However, we
would be correct to assume that no IRQ could happen after we have been
asked to free its associated descriptor.

Is

it arch-dependent?


Nope. Both APIs are arch-agnostic anyway.

I think the pattern dates back in RTAI times and was

needed for so far unused IRQs. Disabling them on device closure blocked
the line for later use under Linux.


We never had this problem with Xeno, since we always relied on the
standard IRQ controllers defined by Linux for managing interrupt lines.
IOW, Linux can undo what Xenomai did wrt IRQ line enabling/disabling.



So the enable is definitely needed and a disable on release should not
cause harm anymore? If that's the case, we could start re-introducing
rtdm_irq_disable before rtdm_irq_free again.

Except for interrupts shared between RT/non-RT, the don't need enable (since they are enabled by Linux already), and probably doesn't fare well with a final disable.


That's the uncommon case by essence, for which a different set of rules already applies anyway.



I'm asking now in case we have to change the usage: we may better do it
early (e.g. with the introduction of Xenomai 2.1), so that the number of
surprises can be kept low when the underlying mechanisms get reworked
later.



--

Philippe.

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