linux-kernel - Re: [PATCH 3/3] usb: cdns3: Enable workaround for USB2.0 PHY Rx compliance test PHY lockup

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Date:   Thu, 27 Aug 2020 16:02:39 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Roger Quadros <rogerq@...com>, Peter Chen <peter.chen@....com>
Cc:     Pawel Laszczak <pawell@...ence.com>,
        Rahul Kumar <kurahul@...ence.com>,
        "nsekhar@...com" <nsekhar@...com>,
        "vigneshr@...com" <vigneshr@...com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 3/3] usb: cdns3: Enable workaround for USB2.0 PHY Rx
 compliance test PHY lockup


Hi,

Roger Quadros <rogerq@...com> writes:
>>>>>>>>> From: Pawel Laszczak <pawell@...ence.com>
>>>>>>>>>
>>>>>>>>> USB2.0 PHY hangs in Rx Compliance test when the incoming packet
>>>>>>>>> amplitude is varied below and above the Squelch Level of Receiver
>>>>>>>>> during the active packet multiple times.
>>>>>>>>>
>>>>>>>>> Version 1 of the controller allows PHY to be reset when RX fail
>>>>>>>>> condition is detected to work around the above issue. This feature
>>>>>>>>> is disabled by default and needs to be enabled using a bit from
>>>>>>>>> the newly added PHYRST_CFG register. This patch enables the workaround.
>>>>>>>>>
>>>>>>>>> As there is no way to distinguish between the controller version
>>>>>>>>> before the device controller is started we need to rely on a DT
>>>>>>>>> property to decide when to apply the workaround.
>>>>>>>>
>>>>>>>> Pawel, it could know the controller version at cdns3_gadget_start,
>>>>>>>> but the controller starts when it tries to bind gadget driver, at
>>>>>>>> that time, it has already known the controller version.
>>>>>>>>
>>>>>>>> For me, the device controller starts is using USB_CONF.DEVEN (Device
>>>>>>>> Enable) through usb_gadget_connect, I am not sure if it is the same
>>>>>>>> with yours.
>>>>>>>>
>>>>>>>
>>>>>>> Yes in device mode driver knows controller version but this
>>>>>>> workaround Must be enabled also in host mode. In host mode the
>>>>>>> controller doesn't have access to device registers. The controller
>>>>>>> version is placed in device register.
>>>>>>>
>>>>>>
>>>>>> You may suggest your design team adding CHIP_VER register at global
>>>>>> register region, it will easy the software engineer life.
>>>>>>
>>>>> >From what I read, this register is only enabling USB2 PHY reset
>>>>>> software control, it needs for all chips with rev 0x0002450D, and the
>>>>>> place you current change is only for 0x0002450D, right?
>>>>>
>>>>> Even I could say that this workaround should be enabled only for Specific USB2
>>>>> PHY  (only 0x0002450D)
>>>>>
>>>>> This bit should not have any impact for Cadence PHY but it can has Impact for third
>>>>> party PHYs.
>>>>>
>>>>
>>>> So, it is related to specific PHY, but enable this specific PHY reset bit is at controller region, why don't
>>>> put this enable bit at PHY region?
>>>
>>> I think this is related to Controller + PHY combination.
>>> The fix for the issue is via a bit in the controller, so it needs to be managed by the
>>> controller driver.
>>>
>>>>
>>>> So, you use controller's device property to know this specific PHY, can controller know this specific
>>>> PHY dynamically?
>>>
>>> Still the PHY will have to tell the controller the enable that bit. How to do that?
>>>
>>> Adding a dt-property that vendors can used was the simplest option.
>>>
>> 
>> Ok, does all controllers with ver 0x0002450D need this fix? I just think
>> if we introduce a flag stands for ver 0x0002450D in case this ver has
>> other issues in future or just using phy reset enable property?
>> 
>> Pawel & Roger, what's your opinion?
>> 
> I think it is best to keep the flags specific to the issue rather than
> a one flag for all issues with a specific version. This way you can
> re-use the flag irrespective of IP version.

I second that. Specially when some SoC-manufacturers may implement ECO
fixes and not change IP revision.

> But best case is that Cadence put a IP revision register in common area as you
> have previously suggested so driver can automatically apply quirks to specific
> versions.

little too late for that :-)

-- 
balbi

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