linux-kernel - Re: [PATCH v3 2/2] usb: dwc3: core: defer probe on ulpi_read

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Date:   Fri, 18 Nov 2022 13:29:03 +0100
From:   Ferry Toth <fntoth@...il.com>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Ferry Toth <ftoth@...londelft.nl>
Cc:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sean Anderson <sean.anderson@...o.com>,
        Liu Shixin <liushixin2@...wei.com>,
        Andrey Smirnov <andrew.smirnov@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] usb: dwc3: core: defer probe on ulpi_read_id
 timeout


On 18-11-2022 03:11, Thinh Nguyen wrote:
> On Thu, Nov 17, 2022, Ferry Toth wrote:
>> Since commit 0f010171
> I don't your update as noted in the v3 change (ie. Greg's suggestions).

Indeed. I seem to have sent in the wrong sha. Sorry about this.

>> Dual Role support on Intel Merrifield platform broke due to rearranging
>> the call to dwc3_get_extcon().
>>
>> It appears to be caused by ulpi_read_id() masking the timeout on the first
>> test write. In the past dwc3 probe continued by calling dwc3_core_soft_reset()
>> followed by dwc3_get_extcon() which happend to return -EPROBE_DEFER.
>> On deferred probe ulpi_read_id() finally succeeded.
>>
>> As we now changed ulpi_read_id() to return -ETIMEDOUT in this case, we
>> need to handle the error by calling dwc3_core_soft_reset() and request
>> -EPROBE_DEFER. On deferred probe ulpi_read_id() is retried and succeeds.
>>
>> Signed-off-by: Ferry Toth <ftoth@...londelft.nl>
>> ---
>>   drivers/usb/dwc3/core.c | 7 ++++++-
>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>> index 648f1c570021..2779f17bffaf 100644
>> --- a/drivers/usb/dwc3/core.c
>> +++ b/drivers/usb/dwc3/core.c
>> @@ -1106,8 +1106,13 @@ static int dwc3_core_init(struct dwc3 *dwc)
>>   
>>   	if (!dwc->ulpi_ready) {
>>   		ret = dwc3_core_ulpi_init(dwc);
>> -		if (ret)
>> +		if (ret) {
>> +			if (ret == -ETIMEDOUT) {
>> +				dwc3_core_soft_reset(dwc);
> I'm not sure if you saw my previous response. I wanted to check to see
> if we need to do soft-reset once before ulpi init as part of its
> initialization.
I missed it but found it now. I will try your suggestion and answer.
> I'm just curious why Andrey Smirnov test doesn't require this change. If
> it's a quirk for this specific configuration, then the change here is
> fine. If it's required for all ULPI setup, then we can unconditionally
> do that for all ULPI setup during initialization.

Yes me too. I can reproduce that when I build kernel and rootfs with 
buildroot there is no issue. But as soon as I add ftrace / bootconfig 
the issue appears and then I can't analyze the flow. It's seems some 
kind of timing / race.

However, I have tried deferring without dwc3_core_soft_reset() (to 
verify if it is just a matter of time) and that doesn't work. dwc3 is 
deferred about 10x and then gives up without phy. So, it's not just the 
time and not just a matter of retrying the test write.

>> +				ret = -EPROBE_DEFER;
>> +			}
>>   			goto err0;
>> +		}
>>   		dwc->ulpi_ready = true;
>>   	}
>>   
>> -- 
>> 2.37.2
>>
> Thanks,
> Thinh