Re: [RFC 2/8] usb: dwc3: core: Register vendor hooks for dwc3-qcom

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On 11/3/2023 8:44 PM, Bryan O'Donoghue wrote:
On 17/10/2023 14:18, Krishna Kurapati wrote:

The following are the requirements aimed in this implementation:

1. When enum in device mode, Glue/core must stay active.

2. When cable is connected but UDC is not written yet, then glue/core
must be suspended.

3. Upon removing cable in device mode, the disconnect event must be
generated and unblock runtime suspend for dwc3 core.

Signed-off-by: Krishna Kurapati <quic_kriskura@xxxxxxxxxxx>


Hi Bryan,

What happens to this code if you

static int count;

1. sleep in dwc3_probe for 10 milliseconds
2. return -EPROBE_DEFER
3. if count++ < 5 goto 1

i.e. if we simulate say waiting on a PHY driver to probe in dwc3_probe()

The vendor hooks are used in __dwc3_set_mode and role_switch_set calls in core and drd files respectively. These are invoked only if we are OTG capable. The drd_work is initialized in core_init_mode which is called at the end of dwc3_probe. If dwc3_probe fails and gets deferred before that, none of the vendor hooks will be fired and dwc3_qcom_probe is also deferred.

However I see that if core_init_mode fails (the cleanup is already done in drd to prevent set_role from getting invoked already), I need to cleanup vendor hooks in error path of dwc3_probe().

and what happens if we introduce a 100 millsecond sleep into dwc3_qcom_probe() - and run a fake disconnect event from dwc3_qcom_probe_core() directly ?

In other words if make it that dwc3_probe() completes and struct dwc3_glue_ops->notify_cable_disconnect() fires prior to dwc3_qcom_probe_core() completing ?

i.e. I don't immediately see how you've solved the probe() completion race condition here.

Just wanted to understand the situation clearly. Is this the sequence you are referring to ?

1. dwc3_probe is successful and role switch is registered properly.
2. added delay after dwc3_qcom_probe_core and before interconnect_init
3. Between this delay, we got a disconnect notificiation from glink
4. We are clearing the qscratch reg in case of device mode and un-registering notifier in case of host mode.

If so, firstly I don't see any issue if we process disconnect event before qcom probe is complete. If we reached this stage, the clocks/gdsc is definitely ON and register accesses are good to go.

If we are in host mode at this point, we would just unregister to usb-core notifier and mark last busy. If we are in device mode, we would just clear the hs_phy_ctrl reg of qscratch. After the 100ms delay you mentioned we would call dwc3_remove anyways and cleanup the vendor hooks. But is the concern here that, what if we enter runtime_suspend at this point ?

Regards,
Krishna,




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