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SubjectRe: [PATCH v20 2/5] usb: dwc3: core: Host wake up support from system suspend
On Thu, Jun 30, 2022 at 06:10:50PM -0700, Matthias Kaehlcke wrote:
> > > dwc3-qcom should wait for dwc3 core to call component_add() and then do
> > > whatever needs to be done once the dwc3 core is registered in the
> > > dwc3-qcom bind callback. Honestly this may all be a little overkill if
> > > there's only two drivers here, dwc3-qcom and dwc3 core. It could
> > > probably just be some callback from dwc3 core at the end of probe that
> > > calls some function in dwc3-qcom.
> > Since the issue we are facing is that the ssphy device links are not ready
> > causing the dwc3 probe not being invoked, can we add an API as Pavan
> > suggested
> > to check if deferred_probe listfor dwc3 device is empty or not andbased on
> > that we can choose to defer our qcomprobe ? In this case, we don't need to
> > touch the dwc3 core driver and would be making changesonly in qcom glue
> > driver.
>
> As mentioned above, it shouldn't be necessary to add component support to
> all the glue drivers. An API to check for deferred probing is an option,
> however there is a possible race condition: When the dwc3-qcom driver checks
> for a deferred probe the core could still be probing, in that situation the
> glue would proceed before the core driver is ready. That could be avoided
> with the component based approach.

The race can happen only if asynchronous probe is enabled, otherwise the
child's probe happens synchronously in of_platform_populate()

OTOH, would the below condition suffice for our needs here? if our device
is not bounded to a driver, we check the state of initcalls and return
either error or -EPROBE_DEFER

diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
index 7b6eff5..519a503 100644
--- a/drivers/usb/dwc3/dwc3-qcom.c
+++ b/drivers/usb/dwc3/dwc3-qcom.c
@@ -722,6 +722,9 @@ static int dwc3_qcom_of_register_core(struct platform_device *pdev)
dev_err(dev, "failed to get dwc3 platform device\n");
}

+ if (!qcom->dwc3->dev.driver)
+ return driver_deferred_probe_check_state(&qcom->dwc3->dev);
+
node_put:
of_node_put(dwc3_np);

Thanks,
Pavan
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