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 00:24:55 +0000
From:   Peter Chen <peter.chen@....com>
To:     Roger Quadros <rogerq@...com>
CC:     Pawel Laszczak <pawell@...ence.com>,
        "balbi@...nel.org" <balbi@...nel.org>,
        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

On 20-08-26 15:49:57, Roger Quadros wrote:
> Peter,
> 
> On 26/08/2020 11:07, Peter Chen wrote:
> > > 
> > > 
> > > > 
> > > > On 20-08-26 04:04:01, Pawel Laszczak wrote:
> > > > > > On 20-08-25 15:00:59, Roger Quadros wrote:
> > > > > > > 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?

-- 

Thanks,
Peter Chen