linux-kernel - Re: [PATCH 2/3] usb: gadget: composite: Split composite reset and disconnect

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Date:   Fri, 8 Jan 2021 22:04:27 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Jack Pham <jackp@...eaurora.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC:     Felipe Balbi <balbi@...nel.org>,
        Wesley Cheng <wcheng@...eaurora.org>,
        "peter.chen@....com" <peter.chen@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH 2/3] usb: gadget: composite: Split composite reset and
 disconnect

Jack Pham wrote:
> Hi Thinh,
>
> On Fri, Jan 08, 2021 at 02:19:30AM +0000, Thinh Nguyen wrote:
>> Hi Wesley,
>>
>> Felipe Balbi wrote:
>>> Hi,
>>>
>>> Wesley Cheng <wcheng@...eaurora.org> writes:
>>>> +void composite_reset(struct usb_gadget *gadget)
>>>> +{
>>>> +	/*
>>>> +	 * Section 1.4.13 Standard Downstream Port of the USB battery charging
>>>> +	 * specification v1.2 states that a device connected on a SDP shall only
>>>> +	 * draw at max 100mA while in a connected, but unconfigured state.
>>> The requirements are different, though. I think OTG spec has some extra
>>> requirements where only 8mA can be drawn max. You need to check for the
>>> otg flag. Moreover, USB3+ spec has units of 150mA meaning the device
>>> can't draw 100mA (IIRC).
>>>
>> We see issue with this patch series. For our device running at SSP, the
>> device couldn't recover from a port reset and remained in eSS.Inactive
>> state.
>>
>> This patch series is already in Greg's usb-testing. Please review and
>> help fix it.
>>
>> We can see the failure once the patch "usb: gadget: configfs: Add a
>> specific configFS reset callback" is introduced.
> Hmm. Does your device use a legacy USB2 PHY (not generic PHY) driver,
> and does it implement the usb_phy_set_power() callback? Because
> otherwise this new configfs_composite_reset() callback would not have
> changed from the original behavior since the newly introduced (in patch
> 1/3) dwc3_gadget_vbus_draw() callback would simply be a no-op if
> dwc->usb2_phy is not present.
>
> If it does turn out to be something with your PHY driver's set_power(),
> it's still puzzling since it's directed to only the usb2_phy, so I'm
> curious how telling it to draw 100mA could affect SSP operation at all.
>
> Thanks,
> Jack

So, I ran some more tests. It seems like this new change affects some
timing in my setup that triggers this failure. I tried to add some
printouts to look into it further, but somehow that reduces the failure
rate significantly. This doesn't seem related to power drawing as it
doesn't update usb2_phy for SSP as you said.

After switching my HW setup, the problem seems to go away. I guess we
can ignore this since the code path looks to be the same as previous.

BR,
Thinh