On 26.05.20 09:04, Martin Kepplinger wrote: > hi all, > > our Librem 5 includes the microchip USB2642 hub with > integrated/connected SD cardcreader (and we connect the baseband modem > to it): https://www.microchip.com/wwwproducts/en/USB2642 > > When we remove the (integrated) SD cardreader entirely (in sysfs), the > Hub suspends as long as the modem doesn't need a connection. But then > the modem fails to *resume* the Hub. Linux xhci host times out and dies > during resuming, which leaves a system without the Hub entirely. You can > see some logs and tests here > https://source.puri.sm/Librem5/linux-next/issues/170#note_89808 (when > scrolling down). > > Microchip says the their product has the following bug which results in > our problem: > https://microchipsupport.force.com/s/article/Device-attached-to-Hub-Downstream-Facing-Port-does-not-Resume-from-Suspend > (that may or may not be the real and only reason for our problem) > > That issue suggests working around it in the HC by somehow > sending "HS SOF as soon as possible after the HS RESUME EOP". > > We use imx8mq and the dwc3 driver for the designware USB hardware that > NXP documents in chapter 11.1.3 of the reference manual: > https://www.nxp.com/products/processors-and-microcontrollers/arm-processors/i-mx-applications-processors/i-mx-8-processors/i-mx-8m-family-armcortex-a53-cortex-m4-audio-voice-video:i.MX8M?tab=Documentation_Tab > > What can we try to change in dwc3 or xhci drivers in order to achieve > sending SOF earlier after resume? > > What else that I don't currently think of could lead to the USB > suspend/resume problem here? For future reference: We've been able to make the Hub resume when not applying any quirks to dwc3. > > > > p.s.: A follow-up for Microchip: The Hub doesn't suspend when the SD > cardreader is connected *without* and SD card inserted (as described > above, we remove the cardreader for testing here). What could cause this? > We've resolved this issue too. When scsi (sd) runtime pm is not enabled by default, it needs to be enabled of course and events_dfl_poll_msecs for the block layer set to 0. scsi sd has until now incomplete support for runtime pm and this addition makes it work, i.e. suspend when not mounted: https://lore.kernel.org/linux-scsi/20200623111018.31954-1-martin.kepplinger@xxxxxxx/T/ the whole USB path is suspended as a consequence - and woken up if opened. martin
