Re: usb: dwc2: Detecting cable disconnection in OTG mode?

[Minas Harutyunyan <Minas.Harutyunyan@synopsys.com>]

Hi Pavel,

On 12/12/2021 5:47 PM, Pavel Hofman wrote:
> Dne 11. 12. 21 v 10:59 Pavel Hofman napsal(a):
>> Dne 11. 12. 21 v 10:55 Pavel Hofman napsal(a):
>>> Hi Minas,
>>>
>>> I am trying to find if dwc2 in OTG mode can pass information to 
>>> gadget functions that the host has been disconnected. I am testing on 
>>> RPi4. In a datasheet for a different dwc2 implementation 
>>> https://urldefense.com/v3/__https://www.mouser.cn/datasheet/2/196/Infineon-xmc4500_rm_v1.6_2016-UM-v01_06-EN-598157.pdf__;!!A4F2R9G_pg!MEHtWBYLNFmrcqrgWFVPEBTCgO8uc0-Csekg1qk6WkiSEqzoGkWH8OMo9aZtgRJGugkkc6Kq$ 
>>> - chapter "16.8.3 Device Disconnection" I found:
>>>
>>>
>>> ===========
>>> The device session ends when the USB cable is disconnected or if the 
>>> VBUS is switched off by the host.
>>> The device disconnect flow is as follows:
>>>
>>> 1. When the USB cable is unplugged or when the VBUS is switched off 
>>> by the host, the device core triggers GINTSTS.OTGInt [bit 2] 
>>> interrupt bit
>>> ============
>>>
>>> I put a printk to core_intr.c:dwc2_handle_otg_intr() which is called 
>>> only from handling the OTGInt interrupt 
>>> https://urldefense.com/v3/__https://elixir.bootlin.com/linux/v5.1.9/source/drivers/usb/dwc2/core_intr.c*L803__;Iw!!A4F2R9G_pg!MEHtWBYLNFmrcqrgWFVPEBTCgO8uc0-Csekg1qk6WkiSEqzoGkWH8OMo9aZtgRJGumkIC5EA$ 
>>> . But this method is not called at all when disconnecting the USB 
>>> cable on RPi4 in gadget mode.
>>>
>>
>> To add, the method dwc2_hsotg_disconnect is called, but after 
>> reconnecting the cable, as part of the gadget reset  when handling 
>> reset interrupts (gintsts & (GINTSTS_USBRST | GINTSTS_RESETDET)) here 
>> https://urldefense.com/v3/__https://elixir.bootlin.com/linux/v5.1.9/source/drivers/usb/dwc2/gadget.c*L3653__;Iw!!A4F2R9G_pg!MEHtWBYLNFmrcqrgWFVPEBTCgO8uc0-Csekg1qk6WkiSEqzoGkWH8OMo9aZtgRJGugg7wbmK$ 
>>
> 
> 
> Maybe the reason for the OTGInt not being thrown at cable disconnect is 
> the fact that RPi4 most likely does not handle USB_OTG_ID signal. I 
> asked about USB_OTG_ID wiring on RPi4 at their forum.
> 
> Nevertheless it turns out that DWC2 throws Suspend interrupt 
> GINTSTS_USBSUSP (11) at cable disconnection on the RPi4, and the gadget 
> composite driver calls suspend hook of struct usb_function. I wonder if 
> implementing the suspend handler would be a solution for other dwc2 
> implementations, or if the audio function should implement also some 
> other handler in order to correctly serve the cable disconnection for 
> all dwc2 implementations.
> 
> Thanks a lot,
> 
> Pavel.
> 
> 
> 
Disconnect event on different platform behave differently. It's depend 
on platform design, PHY, etc. Yes, GINTSTS_USBSUSP (11) at cable 
disconnection can be used to detect disconnect event.

Thanks,
Minas