[Open-graphics] Video interrupt enable/disable

[James Richard Tyrer]

Paul Brook wrote:
>>> On a typical PCI system each device only gets a single interrupt pin (a
>>> PCI bus has 4, but each device is only supposed to use 1), and several
>>> devices share an interrupt line.
>>>
>>> Thus all interrupts should be maskable on the device, and probably
>>> combined into a single output after masking.
>> I'm not a PCI expert.  However, you are talking about the actual
>> physical implementation in PCI.  If masking is required, this would be a
>> function in the PCI interface.  However, IIUC, PCI devices are allowed
>> multiple interrupts -- each PCI device is allowed to use all 4
>> interrupts.  If they share common physical interrupt lines, this is an
>> issue with the PCI interface hardware and driver.
> 
> Each physical card has 4 interrupt pins (usually with a total of 4 shared 
> lines per bus), however each logical PCI device is only allowed to use a 
> single pin.

If you know how this works, they you should correct:

http://en.wikipedia.org/wiki/Peripheral_Component_Interconnect
> 
> IMHO the sync interrupt doesn't need to be different from to any other 
> interrupt.

If the interrupt is the same for sync and service request, then the 
driver will have to read two status register bits to see which interrupt 
is set before the interrupt is serviced and then write back to clear the 
interrupt.

-- 
JRT