Re: [PATCH v2] usb: dwc3: qcom: Defer dwc3-qcom probe if dwc3 isn't probed properly

[Johan Hovold <johan@kernel.org>]

On Fri, Jul 15, 2022 at 06:51:52PM +0530, Krishna Kurapati wrote:
> On SC7180 devices, it is observed that dwc3 probing is deferred
> because device_links_check_suppliers() finds that '88e3000.phy'
> isn't ready yet.
> 
> As a part of its probe call, dwc3-qcom driver checks if dwc3 core
> is wakeup capable or not. If the dwc3 core is wakeup capable, driver
> configures dwc-qcom's power domain to be always ON. Also it configures
> dp/dm interrupts accordingly to support wakeup from system suspend.
> 
> More info regarding the same can be found at:
> commit d9be8d5c5b03 ("usb: dwc3: qcom: Keep power domain on to retain controller status")
> commit 6895ea55c385 ("usb: dwc3: qcom: Configure wakeup interrupts during suspend")
> 
> In the event, dwc3 probe gets deferred and is processed after dwc3-qcom
> probe, driver ends up reading the wakeup capability of dwc3 core as false
> leading to instability in suspend/resume path.
> 
> To avoid this scenario, ensure dwc3_probe is successful by checking
> if appropriate driver is assigned to it or not after the of_platform_populate
> call. If it isn't then defer dwc3-qcom probe as well.
> 
> Fixes: 649f5c842ba3 ("usb: dwc3: core: Host wake up support from system suspend")
> Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>
> ---
> v2: Set return value to EPROBE_DEFER to drop reference to dwc3 node
> 
>  drivers/usb/dwc3/dwc3-qcom.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
> index 7703655..6676b39 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)
> +		ret = -EPROBE_DEFER;
> +
>  node_put:
>  	of_node_put(dwc3_np);

NAK.

We should not be adding hacks like this to the driver.

There are other ways to avoid this, but please take a look at the
following series which makes the problem identified by this patch go
away first:

	https://lore.kernel.org/all/20220802151404.1797-1-johan+linaro@kernel.org

Johan