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

[Krishna Kurapati PSSNV <quic_kriskura@quicinc.com>]

On 8/2/2022 9:40 PM, Johan Hovold wrote:
> 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
Hi Johan,

  Thanks for the review and patches. Agreed that if we are moving 
wakeup-source to glue driver, dwc3 probe getting deferred won't be an issue.

Regards,
Krishna,