linux-kernel - Re: [PATCH v4 2/3] Broadcom USB DRD Phy driver for Northstar2

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Message-ID: <a78f6948-0900-56f9-dc0c-5b161c470847@ti.com>
Date:   Mon, 10 Apr 2017 13:57:07 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Raviteja Garimella <raviteja.garimella@...adcom.com>
CC:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Jon Mason <jonmason@...adcom.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 2/3] Broadcom USB DRD Phy driver for Northstar2

Hi,

On Monday 10 April 2017 12:57 PM, Raviteja Garimella wrote:
> Hi,
> 
> On Mon, Apr 10, 2017 at 10:55 AM, Kishon Vijay Abraham I <kishon@...com> wrote:
>> Hi,
>>
>> On Wednesday 05 April 2017 07:40 PM, Raviteja Garimella wrote:
>>> Hi Kishon,
>>>
>>> On Wed, Apr 5, 2017 at 7:04 PM, Kishon Vijay Abraham I <kishon@...com> wrote:
>>>> Hi Ravi,
>>>>
>>>> On Wednesday 05 April 2017 06:30 PM, Raviteja Garimella wrote:
>>>>> Hi Kishon,
>>>>>
>>>>> On Wed, Apr 5, 2017 at 4:30 PM, Kishon Vijay Abraham I <kishon@...com> wrote:
>>>>>> Hi,
>>>>>>
>>>>>> On Tuesday 28 March 2017 05:57 PM, Raviteja Garimella wrote:
>>>>>>> This is driver for USB DRD Phy used in Broadcom's Northstar2
>>>>>>> SoC. The phy can be configured to be in Device mode or Host
>>>>>>> mode based on the type of cable connected to the port. The
>>>>>>> driver registers to  extcon framework to get appropriate
>>>>>>> connect events for Host/Device cables connect/disconnect
>>>>>>> states based on VBUS and ID interrupts.
>>>>>>
>>>>>> $patch should be phy: phy-bcm-ns2-usbdrd: USB DRD Phy driver for Broadcoms
>>>>>> Northstar2.
>>>>>>
>>>>>
>>>>> Will do.
>>>>>
>>>>>> Sorry for not letting you know this earlier. But I feel the design of the
>>>>>> driver should be changed. Extcon shouldn't be used here. The extcon
>>>>>> notifications should be sent to the consumer driver and the consumer driver
>>>>>> should be responsible for invoking the phy ops.
>>>>>>
>>>>>
>>>>> The consumer drivers here would be a UDC driver (USB device
>>>>> controller), EHCI and OHCI host controller drivers.
>>>>> I was already suggested in UDC driver review to deal with extcon in Phy driver.
>>>>>
>>>>> This phy connects to 2 host controllers, and one device controller.
>>>>> That's the design in Broadcom Northstar2
>>>>> platform. The values of the VBUS and ID pins of this port are
>>>>> determined based on the type of the cable (device cable
>>>>> or host cable). And. phy has to be configured accordingly.
>>>>>
>>>>>> The phy ops being invoked during extcon events doesn't look right.
>>>>>
>>>>> Could you please elaborate on the concern, so that we can think of
>>>>> mitigating those issues in this driver?
>>>>> Since we are dealing with phy init/shutdown in this driver itself, are
>>>>> you okay with moving the extcon handling code
>>>>> out of phy ops ?
>>>>
>>>> yeah, For e.g., ns2_drd_phy_init is part of phy_ops and is being invoked from
>>>> extcon events too. Can a phy which is initialized by a phy consumer (say your
>>>> UDC invokes phy_init) can be shutdown by an extcon event?
>>>>
>>>> Maybe a clear explanation of when phy_ops here will be invoked and when it will
>>>> set using extcon events might help.
>>>>
>>>
>>> Say, we have a USB pendrive which is connected to the DRD port through
>>> a host cable.
>>> Now the PHY will be initialized to be in host mode.
>>> When the pendrive is unplugged, and we now connect the NS2 device to
>>> some linux PC,
>>> now the PHY has to be shutdown, and re-initialized to be in Device mode.
>>>
>>> On unplug event, it is set neither to Host nor Device mode (basically
>>> shutdown). Next time which ever cable is connected, the PHY is
>>> initialized to the respective
>>> mode.
>>>
>>> Please let me know if it's fine to do these initializations outside
>>> phy ops, because those will
>>> be irrelevant for phy consumers (the controllers) as it's anyways
>>> dealt in the phy driver through
>>> extcon.
>>
>> How does the consumer get to know whether they have to operate in host mode or
>> device mode?
>>
> In NS2, we have host controllers and device controller (not OTG/other
> that can switch
> between host and device mode). It's only phy that can be in host/device mode.
> Since both Host Controllers and Device Controller are connected to the same PHY,
> it is based on the extcon logic (the type of cable connected) that PHY
> will be in one
> of the modes host/device and the respective controller will operate.

So at a point of time either the host controller or the device controller will
be active? and the PHY decides which of them should be active? Is that right?

Thanks
Kishon