[PATCH] genirq: Introduce irq_read_line()

Hi Bjorn,

On 24/10/14 18:31, Bjorn Andersson wrote:

On Tue, Oct 21, 2014 at 2:34 AM, Marc Zyngier [off-list ref] wrote:

quoted

Hi all,

On 21/10/14 10:22, Thomas Gleixner wrote:

quoted

On Thu, 4 Sep 2014, Bjorn Andersson wrote:

quoted

On Tue, Aug 19, 2014 at 1:23 PM, Bjorn Andersson
[off-list ref] wrote:

quoted

Introduce the irq_read_line() function to allow device drivers to read
the current logical state of an input when the hardware only exposes
this through status bits in the interrupt controller.

The new function is backed by a new callback function in the irq_chip -
irq_read_line() - that can be implemented by irq_chips that owns such
status bits.

Based on rfc patch from April 2011 by Abhijeet.

Cc: Abhijeet Dharmapurikar <redacted>
Signed-off-by: Bjorn Andersson <redacted>

ping?

Sorry, slipped through the cracks. I was talking about this to Marc
last week and he needs it for yet another reason. He had some thoughts
about the state representation, so I wait for him to comment.

Thanks for putting me in the loop. For the record, here's the RFC I
posted back in June:

Thanks for having a similar problem as me :)

quoted

http://lists.infradead.org/pipermail/linux-arm-kernel/2014-June/266328.html

and the patch implementing a similar concept:
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-June/266331.html

I would prefer to see that you had explicit functions for the various things
that you would like to set and get. It would in my eyes give cleaner client
code, at the cost of a few extra functions.

I don't really like the idea of having a gazillion of accessors for each
individual property. I'd rather have an extensible API.

quoted

Basic idea is that you can read (and possibly write back) various
low-level attributes (pending, masked, active) that an interrupt
controller may implement. Given your use case, we should loose the
checks on the interrupt being forwarded, as this makes little sense
outside of virtualization.

Relaxing the forwarding requirement seems to solve my use cases. May I ask why
your accessors would only be made available for forwarded IRQs - at a framework
level?

This was never intended for wider use, and restricting it to forwarded
interrupts was a concious design decision, as I find the idea of a
device driver messing with the internal state of the interrupt
controller positively repulsive... But hey, the more the merrier.

Stephen Boyd talked about the need to be able to mask/unmask interrupts from
client code in the Qualcomm platform as well - most likely to block wakeup
sources(?)

What's wrong with irq_disable?

quoted

I'm planning to respin the series this week, as I have a number of
changes (there is hardly any need for the various states to be reported
atomically, for example), and a number of bugs have been found.

Sounds good, for clarity I would like them to be explicit separate functions.
But as long as it's not limited to forwarded IRQs we should be able to use it.

I just pushed out a branch:
git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git
irq/irqchip_state

Please let me know if that's useful for you.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...