dwc_otg: switching to device mode at run time hangs the kernel

[ali1234]

Leave USB_OTGID floating if you have a compute module, or on the A/A+, write a 1 in to gusbcfg bit 30 to force device only mode.

Expected result: the pi acts as a USB device.

Actual result: the kernel goes in to an endless interrupt loop:

[   23.151467] WARN::dwc_otg_handle_mode_mismatch_intr:68: Mode Mismatch Interrupt: currently in Device mode
[   23.151467] 
[   23.169536] WARN::dwc_otg_handle_mode_mismatch_intr:68: Mode Mismatch Interrupt: currently in Device mode
[   23.169536] 
[   23.187584] WARN::dwc_otg_handle_mode_mismatch_intr:68: Mode Mismatch Interrupt: currently in Device mode
[   23.187584] 
[   23.205596] INFO: rcu_preempt self-detected stall on CPU { 0}  (t=2101 jiffies g=-287 c=-288 q=1)
[   23.219239] Task dump for CPU 0:
[   23.224791] swapper         R running      0     1      0 0x00000000
[   23.233605] [<c00149b0>] (unwind_backtrace) from [<c0012140>] (show_stack+0x20/0x24)
[   23.246049] [<c0012140>] (show_stack) from [<c0047490>] (sched_show_task+0xac/0x108)
[   23.258562] [<c0047490>] (sched_show_task) from [<c0048450>] (dump_cpu_task+0x2c/0x38)
[   23.271373] [<c0048450>] (dump_cpu_task) from [<c0062854>] (rcu_dump_cpu_stacks+0xb0/0x130)
[   23.284699] [<c0062854>] (rcu_dump_cpu_stacks) from [<c0065dcc>] (rcu_check_callbacks+0x494/0x8b0)
[   23.298730] [<c0065dcc>] (rcu_check_callbacks) from [<c006aebc>] (update_process_times+0x44/0x64)
[   23.312794] [<c006aebc>] (update_process_times) from [<c007a8c4>] (tick_sched_handle+0x58/0x64)
[   23.326761] [<c007a8c4>] (tick_sched_handle) from [<c007aac4>] (tick_sched_timer+0x50/0x94)
[   23.340460] [<c007aac4>] (tick_sched_timer) from [<c006b9d4>] (__run_hrtimer+0x94/0x29c)
[   23.354011] [<c006b9d4>] (__run_hrtimer) from [<c006c3f4>] (hrtimer_interrupt+0x10c/0x2ec)
[   23.367807] [<c006c3f4>] (hrtimer_interrupt) from [<c001cc6c>] (bcm2708_timer_interrupt+0x38/0x48)
[   23.382384] [<c001cc6c>] (bcm2708_timer_interrupt) from [<c005bf68>] (handle_irq_event_percpu+0x5c/0x278)
[   23.397701] [<c005bf68>] (handle_irq_event_percpu) from [<c005c1f4>] (handle_irq_event+0x70/0x8c)
[   23.412358] [<c005c1f4>] (handle_irq_event) from [<c005edf0>] (handle_level_irq+0xb0/0x150)
[   23.426625] [<c005edf0>] (handle_level_irq) from [<c005b83c>] (__handle_domain_irq+0x7c/0xd0)
[   23.441083] [<c005b83c>] (__handle_domain_irq) from [<c000f474>] (handle_IRQ+0x2c/0x30)
[   23.454997] [<c000f474>] (handle_IRQ) from [<c0008510>] (asm_do_IRQ+0x18/0x1c)
[   23.468115] [<c0008510>] (asm_do_IRQ) from [<c053b678>] (__irq_svc+0x38/0xd0)
[   23.478265] Exception stack(0xc703bc38 to 0xc703bc80)
[   23.486278] bc20:                                                       00000000 0000000a
[   23.500196] bc40: c082fbc0 c07e0f48 c0025d94 c703a000 00000000 00000202 00000000 c081a09c
[   23.514042] bc60: c07e7138 c703bccc c703bc80 c703bc80 c00257d0 c00257d4 60000113 ffffffff
[   23.527934] [<c053b678>] (__irq_svc) from [<c00257d4>] (__do_softirq+0xb8/0x338)
[   23.541055] [<c00257d4>] (__do_softirq) from [<c0025d94>] (irq_exit+0xb4/0x108)
[   23.554091] [<c0025d94>] (irq_exit) from [<c005b844>] (__handle_domain_irq+0x84/0xd0)
[   23.567657] [<c005b844>] (__handle_domain_irq) from [<c000f474>] (handle_IRQ+0x2c/0x30)
[   23.581399] [<c000f474>] (handle_IRQ) from [<c0008510>] (asm_do_IRQ+0x18/0x1c)
[   23.594326] [<c0008510>] (asm_do_IRQ) from [<c053b678>] (__irq_svc+0x38/0xd0)
[   23.604386] Exception stack(0xc703bd30 to 0xc703bd78)
[   23.612316] bd20:                                     f2980008 00000031 00000001 00000000
[   23.626112] bd40: 00000000 00000000 c71a7000 c0819fb8 c724a8a0 c081a09c c07e7138 c703bdac
[   23.639879] bd60: 00000030 c703bd78 c03c6848 c03c45cc 60000113 ffffffff
[   23.649361] [<c053b678>] (__irq_svc) from [<c03c45cc>] (dwc_otg_driver_probe+0x114/0x7b0)
[   23.663140] [<c03c45cc>] (dwc_otg_driver_probe) from [<c0358b18>] (platform_drv_probe+0x3c/0x6c)
[   23.677559] [<c0358b18>] (platform_drv_probe) from [<c0357500>] (driver_probe_device+0x100/0x224)
[   23.692187] [<c0357500>] (driver_probe_device) from [<c03576c0>] (__driver_attach+0x9c/0xa0)
[   23.706439] [<c03576c0>] (__driver_attach) from [<c0355a0c>] (bus_for_each_dev+0x64/0x98)
[   23.720405] [<c0355a0c>] (bus_for_each_dev) from [<c0356fc4>] (driver_attach+0x28/0x30)
[   23.734175] [<c0356fc4>] (driver_attach) from [<c0356c3c>] (bus_add_driver+0xe8/0x1e8)
[   23.747873] [<c0356c3c>] (bus_add_driver) from [<c0357bd0>] (driver_register+0x88/0x104)
[   23.761748] [<c0357bd0>] (driver_register) from [<c0358a04>] (__platform_driver_register+0x58/0x6c)
[   23.776604] [<c0358a04>] (__platform_driver_register) from [<c07afce8>] (dwc_otg_driver_init+0x5c/0x118)
[   23.791887] [<c07afce8>] (dwc_otg_driver_init) from [<c0008730>] (do_one_initcall+0x90/0x1dc)
[   23.806216] [<c0008730>] (do_one_initcall) from [<c0783e04>] (kernel_init_freeable+0xf0/0x1bc)
[   23.820696] [<c0783e04>] (kernel_init_freeable) from [<c0531cfc>] (kernel_init+0x18/0xfc)
[   23.834769] [<c0531cfc>] (kernel_init) from [<c000eb48>] (ret_from_fork+0x14/0x20)
[   23.848324] WARN::dwc_otg_handle_mode_mismatch_intr:68: Mode Mismatch Interrupt: currently in Device mode
[   23.848324] 
[   23.868236] WARN::dwc_otg_handle_mode_mismatch_intr:68: Mode Mismatch Interrupt: currently in Device mode

[P33M]

"If it is not tested, it does not work".

Device mode using the dwc_otg driver stack hasn't been tried since day 0 of release - I am not surprised that there are serious bugs with the implementation. In particular the FIQ implementation is certain to mess up the handling of device mode interrupts, as certain critical functions/protections have not been implemented on the PCD driver.

There are a number of ways that this can be resolved, all of which require significant engineering time.

1. Bugfix the PCD driver. Made an order of magnitude more complicated due to the inclusion of the FIQ code.
2. Use the upstream dwc2 driver in gadget mode - this in theory "should work" but hasn't really been tested in device mode. The hardware is similar to the type underneath the s3c_hsotg driver in upstream and there is an ongoing effort to consolidate both codebases. This would be the ideal solution if you just require device mode.
3. Port the FIQ code to the dwc2 upstream driver and nobble it in gadget mode - again, requiring engineering hours. This would result in functional device and host modes.

[nanosonde]

I have seen a lot of changes to the DWC2 gadget driver in branch rpi-4.0.y.
Is the FIQ implmentation still an issue?

[Ruffio]

The error/warning still occurs on latest Jessie Lite 4.4 when working with the onboard wifi module on RPi3 , take a look here: raspberrypi/firmware#630

[Ruffio]

@ali1234 has your issue been resolved? If yes, then please close this issue.

[P33M]

Gadget (aka device mode) is primarily supported by the upstream dwc2 driver. dwc_otg should only be used for host mode.