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

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Message-ID: <9fbef986-721c-05aa-28a1-4c49016fe2ca@ti.com>
Date:   Mon, 10 Apr 2017 10:55:37 +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 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?

Thanks
Kishon