[U-Boot] The purpose of enabling CONFIG_PCI_BOOTDELAY

[Stefan Roese <sr@denx.de>]

On Wednesday 24 March 2010 22:34:59 Andrew Dyer wrote:
> >> What is the purpose of CONFIG_PCI_BOOTDELAY? I am using uboot version
> > 
> > Adding a delay so the PCI controllers can come up and stabilize.
> > 
> >> Specifically in my case, all the resets on my board have occurred well
> >> before (500 msec) this portion of the code would execute, so it would
> >> seem safe to say that any peripherals like PCI controllers would be
> >> satisfied reset-wise.
> > 
> > 500ms is not safe. We have seen cases (for example on 440SP / 440SPe)
> > where 5...10 seconds (!) were needed.
> 
> I've seen this as well, so I agree that 500ms seems reasonable for a
> general value.  Per the PCI 2.3 spec, the time is supposed to be min.
> 100mS.

Per PCI 2.2, the PCI target must respond to config accesses within 2^25 clock 
cycles after #RST is de-asserted (PCI System Architecture, fourth edition, 
page 321). With 33MHz this is approx. 1 second.

Cheers,
Stefan

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