dwc2: RPi 3 B plus - USB mass storage boot broken

[Stefan Wahren]

Am 29.06.21 um 13:37 schrieb Stefan Wahren:
> Hi,
>
> i noticed more fallout connected to the recent fw_devlink changes in
> Linux 5.13. Since fw_devlink=on the Raspberry Pi 3 B Plus
> (multi_v7_defconfig, 32 bit) is unable to boot from USB because the dwc2
> driver probe too late and the kernel waits endlessly for the rootfs.
> Switching fw_devlink back to permissive makes the dwc2 driver probe
> earlier and make USB mass storage boot work again.
>
> Here are some dmesg extracts taken from a Raspberry Pi 3 B Plus (5.13,
> multi_v7_defconfig, booting from SD card to show good and bad case):
>
> fw_devlink=permissive
>
> [    2.198105] calling  dwc2_platform_driver_init+0x0/0x10 @ 1
> [    2.198663] initcall dwc2_platform_driver_init+0x0/0x10 returned 0
> after 529 usecs
> [    4.156494] dwc2 3f980000.usb: supply vusb_d not found, using dummy
> regulator
> [    4.174514] dwc2 3f980000.usb: supply vusb_a not found, using dummy
> regulator
> [    4.242973] dwc2 3f980000.usb: DWC OTG Controller
> [    4.259505] dwc2 3f980000.usb: new USB bus registered, assigned bus
> number 1
> [    4.278483] dwc2 3f980000.usb: irq 66, io mem 0x3f980000
> [    4.759700] usb 1-1: new high-speed USB device number 2 using dwc2
> [    5.359793] usb 1-1.1: new high-speed USB device number 3 using dwc2
> [    5.899703] usb 1-1.2: new low-speed USB device number 4 using dwc2
> [    6.149705] usb 1-1.1.3: new low-speed USB device number 5 using dwc2
> [    6.629761] usb 1-1.1.1: new high-speed USB device number 6 using dwc2
>
> fw_devlink=on
>
> [    2.198579] calling  dwc2_platform_driver_init+0x0/0x10 @ 1
> [    2.199021] initcall dwc2_platform_driver_init+0x0/0x10 returned 0
> after 416 usecs
> [    7.693987] dwc2 3f980000.usb: supply vusb_d not found, using dummy
> regulator
> [    7.694228] dwc2 3f980000.usb: supply vusb_a not found, using dummy
> regulator
> [    7.747111] dwc2 3f980000.usb: DWC OTG Controller
> [    7.747152] dwc2 3f980000.usb: new USB bus registered, assigned bus
> number 1
> [    7.747192] dwc2 3f980000.usb: irq 66, io mem 0x3f980000
> [    8.179985] usb 1-1: new high-speed USB device number 2 using dwc2
> [    8.749920] usb 1-1.1: new high-speed USB device number 3 using dwc2
> [    9.179900] usb 1-1.2: new low-speed USB device number 4 using dwc2
> [    9.409951] usb 1-1.1.3: new low-speed USB device number 5 using dwc2
> [    9.849927] usb 1-1.1.1: new high-speed USB device number 6 using dwc2
>
> Unfortunately i wasn't able to find the root cause for this delay of 3
> seconds during boot. I noticed that usb_phy_generic_init is called very
> late. Maybe this is related.

I was able to investigate this further. The Raspberry Pi has a PHY
defined in device tree ( compatible = "usb-nop-xceiv", bcm283x.dtsi )
and in arm/multi_v7_defconfig the relevant driver is compiled as a module.

The dwc2 platform code attempt to find the optional PHY. With
fw_devlink=permissive the dwc2 driver seems to fail getting the PHY and
proceed. But with fw_devlink=on the dwc2 driver seems to go the
EPROBE_DEFER path and wait endlessly for the PHY driver which isn't
built into the kernel. This PHY handling was a troublemaker in the past [1]

So there are two workarounds to avoid this issue with fw_devlink=on:

a) make CONFIG_NOP_USB_XCEIV=y for multi_v7_defconfig
b) remove the usb-nop-xceiv PHY from the device tree

But it would be nice to have a clean solution.

Best regards
Stefan

[1] -
https://patchwork.kernel.org/project/linux-arm-kernel/patch/20180112101223.3661181-1-arnd@arndb.de/

>
> Best regards
> Stefan
>
>