EHCI: read status register is very slow in ehci_irq

[Ming Lei <tom.leiming@xxxxxxxxx>]

Hi,

I found on my machine(lenovo T410), most of time only reading the status
register in the entry of ehci_irq may take 2~4 microseconds, and sometimes
it is extremely slow and the read can consume > 100 microseconds.

I measure the time by adding two trace events around the below line in
entry of ehci_irq().

         status = ehci_readl(ehci, &ehci->regs->status)

Looks it should be a platform-dependent issue and I didn't
observe that on some arm platform.

Could anyone give a hint about the problem?

Thanks,
-- 
Ming Lei
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