linux-kernel - Re: [PATCH v20 2/5] usb: dwc3: core: Host wake up support from system suspend

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Date:   Fri, 1 Jul 2022 15:45:26 +0530
From:   Pavan Kondeti <quic_pkondeti@...cinc.com>
To:     Matthias Kaehlcke <mka@...omium.org>
CC:     Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Pavan Kondeti <quic_pkondeti@...cinc.com>,
        "Bjorn Andersson" <bjorn.andersson@...aro.org>,
        Felipe Balbi <balbi@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Doug Anderson <dianders@...omium.org>,
        "Mathias Nyman" <mathias.nyman@...el.com>,
        <devicetree@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-pm@...r.kernel.org>, <quic_ppratap@...cinc.com>,
        <quic_vpulyala@...cinc.com>
Subject: Re: [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