Re: [Xenomai] How to properly steal the interrupt line of a linux device from rtdm driver ?

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On Mon, Dec 22, 2014 at 02:07:48PM -0500, Lennart Sorensen wrote:
> On Mon, Dec 22, 2014 at 12:39:01PM +0100, tbultel@free.fr wrote:
> > Hi,
> > 
> > On a x86 machine, we historically had an issue due to a conflict on IRQ18,
> > between the rtcan_ixx_pci driver and uhci-hcd.
> > It was not possible to workaround it, by switching the card to another slot.
> > 
> > As the machine has 6 USB ports, and we could afford losing 2 of them, 
> > we decided to disable the USB controllerthat uses the IRQ18, by adding:
> > 
> > request_irq(chip->irq_num, fake_irq_handler, 0, "ixxat_irq_requested", chip)
> > 
> > ... in the code of the rtcan_ixx_pci driver, before calling rtcan_sja1000_register.
> > 
> > And it worked fine, because the usb driver was loaded later, as kernel module,
> > and as the IRQ is not flagged as shared, it does not get it. 
> > The "fake" handler does nothing but returns IRQ_NONE.
> > 
> > 
> > It worked until today, because we now want to boot on USB, and therefore the USB drivers must
> > be builtin.
> > 
> > 
> > Thus, I am attempting to hack a little more, by unregistering all the linux IRQs handlers
> > of IRQ18, before registering the fake handler in place.
> > 
> > I have taken __free_irq as a base, and written a free_irq_force(unsigned int irq)
> > that does not need a devid, because I want to unregister all devices.
> > The function can be summarized as "desc->action = NULL",
> > but I kept all the things around.
> > 
> > I checked that the action list is empty after the call, but for some reason, that does not work.
> > If I plug an USB keyboard, the IRQ happens again, and I am getting a:
> > 
> > Xenomai: xnintr_shirq_handler: IRQ18 not handled. Disabling IRQ line.
> > 
> > ... and the USB keyboard works. My fake handler is not called, either.
> > 
> > I am a little puzzled, and do not understand what I am missing. It sounds just like I modified the wrong action list,
> > or if it was cached somewhere else.
> 
> You should be able to unbind the USB driver from that particular interface
> after boot before loading the rtdm driver.
> 
> Of course any machine made like my desktop would be hopeless since all
> the USB ports are on a single device and share 1 IRQ between all 10 ports.
> Can't do anything there.

I had this exact problem when trying RTnet on an Atom board, and as
a matter of fact, as indicated in Xenomai troubleshooting guide
here:
https://xenomai.org//2014/06/what-if-xenomai-and-linux-devices-share-the-same-irq/

there is something you can do: you can enable MSI if the PCI device
supports them.

-- 
					    Gilles.