Re: XT-PIC interrupts blocked by usbserial ? [Was Re: Intel ICH9M bug : sata unusable with usbserial]

[Mark Lord <kernel@teksavvy.com>]

On 11-03-03 02:06 PM, Alan Stern wrote:
> On Thu, 3 Mar 2011, Mark Lord wrote:
> 
>> Mmm.. I missed that part.  Very curious, that.
>> I wonder if it could be some issue with how the interrupt controller is set up.
>>
>> Oh the other hand, this USB-GPS is probably a "full-speed" (slow) device,
>> using the UHCI interface rather than EHCI.
>>
>> The uhci_irq() handler (in uhci-hcd.c) appears to always return IRQ_HANDLED,
>> even when it didn't actually handle an IRQ.  If I'm reading the code correctly,
>> then that's a bug, and could cause this issue given the "right" peripheral
>> (eg. your USB-GPS).
>>
>> I wonder if uhci_irq() can be a bit more clever and only set IRQ_HANDLED
>> for interrupts that it actually had to handle?  Or am I reading it wrong?
> 
> Evidently you didn't see these lines near the start of the routine:
> 
> 	status = inw(uhci->io_addr + USBSTS);
> 	if (!(status & ~USBSTS_HCH))	/* shared interrupt, not mine */
> 		return IRQ_NONE;

No, I saw those.  But I don't blindly trust comments.  :)

To me, those lines say, "if nothing is active on our bus, then return IRQ_NONE".
With the USB-GPS, the bus probably always as "something active",
even if no URBs have been received at that instant in time.

But I don't have the UHCI spec handy to check right now.

Remember.. there IS a bug here somewhere, so old assumptions
do need to be reexamined to find the darned thing.

Cheers