[Open-graphics] Video interrupt enable/disable

[James Richard Tyrer]

Paul Brook wrote:
>> Perhaps it would be even simpler to have two interrupts.  One as you
>> describe -- a sync interrupt -- which could not be turned off,  A second
>> for a service request which would be triggered by firmware on the board
>> or the DMA controller.
>>
>> Then the issue of turning the sync interrupt off and on is moved to the
>> driver since the APIC Intel acronym == Advanced Programmable Interrupt
>> Controller) on the motherboard already has the hardware to turn off
>> (ignore) an interrupt.
> 
> 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.

-- 
JRT