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

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Date:   Mon, 10 Apr 2017 12:57:14 +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 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.

> Thanks
> Kishon