Re: Interrupt Disable bit

[Matt Kaufman <mek@sco.com>]

O'Shea, David J wrote:
> The configuration software (BIOS or OS) would disable the generation of
> interrupts,
> unless a driver or opROM enables them in an OS or BIOS POST.
>  
> e.g.  Device interrupt generation is disabled, an opROM loads and the device
> opROM
> enables interrupts via the command register.
>  
> e.g.  Device interrupt generation is disabled by BIOS in POST, and an OS
> loads.  The
> OS loads a device driver for the for the device, and in finding an
> appropriate device driver,
> either enables the interrupt for the PCI device on driver load, or enables
> the interrupt for
> PCI device when the driver uses the OS IRQ handler registration mechanism.

Sigh. Is this register mandatory? Sorry don't have PCI 2.3 handy.
>  
> The intent is to prevent devices from generating IRQ's until they have a
> device driver
> loaded that can handle them, since IRQ's are shared.    Otherwise, a device
> may not
> be using its IRQ, but since the IRQ is generated - and shared- with other
> devices,
> those device see unnecessary calls to their IRQ handlers, as the software
> system searches
> for the owner of the IRQ event.   (But there wasn't one, becuase no driver
> is loaded,
> or the driver isn't using the IRQ....)

Not sure the gain's really worth it; sharing interrupts is never great, but
this seems like a corner enough case not to have warranted a spec change.
>  
> Allowing the software subsystem to disable IRQ generation in the device
> solves the issue-
> and that is the point of the Interrupt Disable bit in the command register.
>  
> -David O'Shea
> Enterprise Products and Services Division, Intel Corp.
> 
> -----Original Message-----
> From: Jim Lindeman [mailto:JLindeman@JNI.com]
> Sent: Thursday, November 14, 2002 11:43 AM
> To: pci-sig@znyx.com
> Subject: Interrupt Disable bit
> 
> 
> Hi,
>  
> Does anyone know how the Interrupt Disable bit in the Command register,
> introduced in PCI 2.3 is intended to be used?
>  
>  
> Thanks,
>  
> Jim Lindeman
> Principal Engineer, ASICs
> JNI Corporation
> 45365 Northport Loop West
> Fremont, CA 94538-6417  
> direct +1.510.360.4714
> fax +1.510.252.0123
> jlindeman@jni.com <mailto:jlindeman@jni.com> 
> www.jni.com <http://www.jni.com> 
>       
> 

-- 
Matt Kaufman
mek@caldera.com
Manager, Device Interfaces Group
The SCO Group, Inc., Murray Hill, NJ   VOX: 908 790 2297    FAX: 908 790 2426