linux-kernel - Re: [PATCH v3 3/5] dt/bindings: Add a new property to DA8xx USB PHY

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Message-ID: <8e3c9209-9db0-c288-5b3d-3d29f1571e47@ti.com>
Date:   Thu, 3 Nov 2016 23:20:16 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Alexandre Bailon <abailon@...libre.com>, <david@...hnology.com>,
        <b-liu@...com>, <balbi@...nel.org>
CC:     <khilman@...libre.com>, <linux-kernel@...r.kernel.org>,
        <linux-usb@...r.kernel.org>, <nsekhar@...com>
Subject: Re: [PATCH v3 3/5] dt/bindings: Add a new property to DA8xx USB PHY

Hi,

On Thursday 03 November 2016 10:56 PM, Alexandre Bailon wrote:
> On 11/03/2016 05:34 PM, Kishon Vijay Abraham I wrote:
>> Hi,
>>
>> On Thursday 03 November 2016 08:56 PM, Alexandre Bailon wrote:
>>> The USB PHY is able to operate in OTG, host or peripheral.
>>> Some board may be wired to work act only as host or peripheral.
>>> In such case, the dr_mode property of controller must be set to
>>> host or peripheral. But doing that will also configure the PHY
>>> in host or peripheral mode whereas OTG is able to detect which
>>> role the USB controller should take.
>>> The PHY's host or peripheral mode are actually only useful when
>>> hardware doesn't allow OTG to detect it's role.
>>>
>>> Add the usb20_force_mode property to force the PHY to operate
>>> in host or peripheral mode.
>>
>> I think we do just that if we populate dr_mode with host or peripheral. Why do
>> we need another property to control dr_mode property?
> Because the phy doesn't work correctly when it is in host or
> device mode.

That would be the same even with usb20_force_mode property. How does
usb20_force_mode property help?

Thanks
Kishon

>>> When usb20_force_mode is used, dr_mode should also be configured
>>> to host or peripheral.
>>> The controller uses dr_mode to configure itself, but the phy use
>>> it to get the mode to use to configure the PHY mode.
>>>
>>> Signed-off-by: Alexandre Bailon <abailon@...libre.com>
>>> ---
>>>  Documentation/devicetree/bindings/phy/phy-da8xx-usb.txt | 5 +++++
>>>  1 file changed, 5 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/phy/phy-da8xx-usb.txt b/Documentation/devicetree/bindings/phy/phy-da8xx-usb.txt
>>> index c26478b..9fc87fb 100644
>>> --- a/Documentation/devicetree/bindings/phy/phy-da8xx-usb.txt
>>> +++ b/Documentation/devicetree/bindings/phy/phy-da8xx-usb.txt
>>> @@ -4,6 +4,11 @@ Required properties:
>>>   - compatible: must be "ti,da830-usb-phy".
>>>   - #phy-cells: must be 1.
>>>  
>>> +Optional properties:
>>> +- usb20-force-mode: Force the phy to operate in same mode than the USB OTG controller.
>>> +		    It should only be defined if the hardware is not capable correctly
>>> +		    detect the role of USB by using VBUS and ID pin.
>>
>> From what I understand from the previous patch, if VBUS sense and the session
>> end comparator is enabled, the controller can work in host mode or device mode.
> I but VBUS sense and and session end comparator only seems to work when
> the phy is in otg mode.
> In host mode, the phy stop to work after the first disconnect.
> In device mode, the phy never detect a disconnect.
> In otg mode, these issues go away.
> I'm working on workaround for both of them but I think it is
> better to keep the phy in otg when it is possible.
>>
>> Thanks
>> Kishon
>>
> Thanks,
> Alexandre
>