Re: PCI service interrupt handlers & access to PCI config space

["Pali Rohár" <pali@kernel.org>]

On Tuesday 13 April 2021 00:09:20 Keith Busch wrote:
> On Mon, Apr 12, 2021 at 04:04:51PM +0200, Pali Rohár wrote:
> > On Sunday 11 April 2021 20:25:55 Keith Busch wrote:
> > > On Sat, Apr 10, 2021 at 06:26:22PM +0200, Lukas Wunner wrote:
> > > > 
> > > > 1.5 sec is definitely too long.  This sounds like a quirk of this
> > > > specific hardware.  Try to find out if the hardware can be configured
> > > > differently to respond quicker.
> > > 
> > > While 1.5 sec is long, pcie spec's device control 2 register has an option to
> > > be even longer: up to 64 seconds for a config access timeout! I'm not sure of
> > > the reasoning to allow something that high, but I think the operating system
> > > would be not be too happy with that.
> > 
> > So what can we do in this case? On single core CPU it means that raw
> > spin lock would completely block any operation on CPU for 64 seconds.
> 
> I don't think it would work here. I'm just saying that while 1.5s config
> access is quite long, the spec provides an option where times exceeding
> that are expected.
> 
> I have never seen a device configured that way, though. The completion
> timeouts are usually set in milliseconds.
> 
> > Do you know what is the timeout for other registers?
> 
> The Device Control Register 2 timeout value is the setting for all
> non-posted requests.

Root Bridge of PCIe controller is seen by lspci as:

  DevCtl2: Completion Timeout: 50us to 50ms, TimeoutDis- LTR+ 10BitTagReq- OBFF Disabled, ARIFwd-
           AtomicOpsCtl: ReqEn- EgressBlck-

So it does not look like that Device Control 2 is configured with higher
delays.