linux-kernel - Re: [PATCH v1 1/1] usb: ulpi: defer ulpi_register on ulpi_read

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Date:   Thu, 10 Nov 2022 13:45:27 +0100
From:   Ferry Toth <fntoth@...il.com>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
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>
Subject: Re: [PATCH v1 1/1] usb: ulpi: defer ulpi_register on ulpi_read_id
 timeout

(sorry sent html with previous attempt)

On 10-11-2022 01:06, Thinh Nguyen wrote:
> Hi Ferry,
>
> On Wed, Nov 09, 2022, Ferry Toth wrote:
>> Since commit 0f010171
>> 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() on the first test write failing
>> with -ETIMEDOUT. Currently ulpi_read_id() expects to discover the phy via
>> DT when the test write fails and returns 0 in that case even if DT does not
>> provide the phy. Due to the timeout being masked dwc3 probe continues by
>> calling dwc3_core_soft_reset() followed by dwc3_get_extcon() which happens
>> to return -EPROBE_DEFER. On deferred probe ulpi_read_id() finally succeeds.
>>
>> This patch changes ulpi_read_id() to return -ETIMEDOUT when it occurs and
>> catches the error in dwc3_core_init(). It handles the error by calling
>> dwc3_core_soft_reset() after which it requests -EPROBE_DEFER. On deferred
>> probe ulpi_read_id() again succeeds.
>>
>> Signed-off-by: Ferry Toth<ftoth@...londelft.nl>
>> ---
>>   drivers/usb/common/ulpi.c | 5 +++--
>>   drivers/usb/dwc3/core.c   | 5 ++++-
>>   2 files changed, 7 insertions(+), 3 deletions(-)
>>
> Can you split the dwc3 change and ulpi change to separate patches?

Thanks for your comments.

I will send v2

>> diff --git a/drivers/usb/common/ulpi.c b/drivers/usb/common/ulpi.c
>> index d7c8461976ce..d8f22bc2f9d0 100644
>> --- a/drivers/usb/common/ulpi.c
>> +++ b/drivers/usb/common/ulpi.c
>> @@ -206,8 +206,9 @@ static int ulpi_read_id(struct ulpi *ulpi)
>>   
>>   	/* Test the interface */
>>   	ret = ulpi_write(ulpi, ULPI_SCRATCH, 0xaa);
>> -	if (ret < 0)
>> -		goto err;
>> +	if (ret < 0) {
>> +		return ret;
>> +	}
>>   
>>   	ret = ulpi_read(ulpi, ULPI_SCRATCH);
>>   	if (ret < 0)
>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>> index 648f1c570021..e293ef70039b 100644
>> --- a/drivers/usb/dwc3/core.c
>> +++ b/drivers/usb/dwc3/core.c
>> @@ -1106,8 +1106,11 @@ static int dwc3_core_init(struct dwc3 *dwc)
>>   
>>   	if (!dwc->ulpi_ready) {
>>   		ret = dwc3_core_ulpi_init(dwc);
>> -		if (ret)
>> +		if (ret) {
>> +			dwc3_core_soft_reset(dwc);
> We shouldn't need to do soft reset here. The controller shouldn't be at
> a bad/incorrect state at this point to warrant a soft-reset. There will
> be a soft-reset when it goes through the initialization again.

It doesn't go through the initialization again unless we set 
-EPROBE_DEFER. And when we make ulpi_read_id() return -EPROBE_DEFER it 
will goto err0 here, so skips dwc3_core_soft_reset.

Do you mean you prefer something like:

if (ret) {

     if (ret == -ETIMEDOUT) ret = -EPROBE_DEFER;

     else goto err0;

}

>> +			ret = -EPROBE_DEFER;
> We shouldn't automatically set every error status to correspond to
> -EPROBE_DEFER. Check only the approapriate error codes (-ETIMEDOUT +
> any other?).
Other could be -ENOMEM. I think no need to do any new handling for that.
>>   			goto err0;
>> +		}
>>   		dwc->ulpi_ready = true;
>>   	}
>>   
>> -- 
>> 2.34.1
>>
> Thanks,
> Thinh