Re: EHCI and MUSB do not discover devices without CONFIG_PM

[Ladislav Michl <ladis-6z/3iImG2C8G8FEW9MqTrA@public.gmane.org>]

Hi Greg,

On Tue, Nov 28, 2017 at 08:33:28AM +0100, Greg KH wrote:
> On Mon, Nov 27, 2017 at 11:08:33PM +0100, Ladislav Michl wrote:
> > Hi there,
> > 
> > USB hosts do not discover any connected device on OMAP3 based board
> > with CONFIG_PM=n. Just enabling this option is enough to restore working
> > behaviour. Nothing unusual in log. Tested 4.14.2 and 4.15-rc1. I know
> > a lot of stuff depends on CONFIG_PM, but is this expected behaviour?
> > Neither EHCI nor MUSB is working without CONFIG_PM.
> 
> What bus type is your controllers on?  PCI?  platform?  Something else?

Platform controllers inside OMAP3630 Soc.

> And yes, perhaps this is to be expected, why would you not want
> CONFIG_PM to be enabled?  :)

For a start, I know Linux is general purpose OS and I know I cannot expect
low latency or low jitter when dealing with interrupts.

Original problem is described here:
https://www.spinics.net/lists/linux-omap/msg140081.html

Shortly, with CONFIG_PM jitter of GPIO interrupt is about 350us which
renders IR receiver unuseable - is cannot reliably decode IR protocol
(gpio-ir-recv is used). With CONFIG_PM disabled, jitter is around 30us
and that's enough to make IR decoders work.

And as I was unable to fix it, nor anyone provided useful hint, I though
I could work around problem from another side. And here we are...

Thank you,
	ladis
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