Re: [linux-usb-devel] pegasus + MediaGX: Oops in khubd, the continuing story?

[Alan Cox]

> The Oops'es are mostly in the khubd process, but they sometimes appear in other
> programs (insmod, ifconfig). They always lead to an immedate panic, and nothing

I suspect the ohci driver currently. I've been reviewing it a little and it
is full of code written by someone who does not know about pci write posting.

Specifically

	writel(value, pciaddr)

is a queued operation. So 

	writel(value, foo)
	delay
	real(foo)

might not do the writel into the delay is over or during it. PCI makes 
guarantees that

-	writes will go out in order and will be merged only if prefetchable set
-	multiple writes to the same addr will remain multiple writes
-	reads will not complete until the writes do

This applies in both directions - bus mastering nasties abound notably

	writel(STOP, reg->dmactrl)
	kfree(buffer)

is dangerous 

	You have to do

	writel(STOP, reg->dmactrl);
			[posted]
	readl(reg->dmactrl)
			[read forces write, read reply will follow any DMA
			 pending the other way]

I've not attempted to fix it yet