On Tue, Nov 28, 2017 at 10:30:54AM +0100, Greg KH wrote: > On Tue, Nov 28, 2017 at 09:57:51AM +0100, Ladislav Michl wrote: > > 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. > > Well, it's the best latency of any other OS out there :) Indeed, with CONFIG_PM=n... And that makes it the only OS without USB support out there :) > Anyway, if you want guaranteed response time, you are going to have to > use the RT patchset, no matter what. Otherwise you have the potential > to have bad jitter at times. That will not help, as jitter is comming from some part of SoC sleeping... > > 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. > > bit-banging an ir decoder, ugh, you are in for a world of hurt. Can't > you put a chip on the device that does this for you in hardware? OMAP has DM timer which can be externally trigered on edge. Perfect for that purpose. But I cannot pinmux its input as hw designers did poor job. And there are thousands of devices deployed. So it is about a lot of soldering or providing software solution. > Anyway, good luck! A little pointer would increase "luck" by several order of magnitudes. Thank you, ladis -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
