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? I'm happy for any hint, question or thought about this and hope that this is useful for others too. thanks, martin 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?
