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

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Message-ID: <CAEHZuqMLDssCjka-yArKE8H8S-3_rvJiwO4gh=CYYa1NwCu1zg@mail.gmail.com>
Date:   Mon, 10 Apr 2017 14:00:11 +0530
From:   Raviteja Garimella <raviteja.garimella@...adcom.com>
To:     Kishon Vijay Abraham I <kishon@...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 Mon, Apr 10, 2017 at 1:57 PM, Kishon Vijay Abraham I <kishon@...com> wrote:
> 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?
>

Yes

Thanks,
Ravi

> Thanks
> Kishon