linux-kernel - Re: [RFC][PATCH 2/3] usb: roles: Add usb role switch notifier.

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Date:   Thu, 3 Oct 2019 22:56:24 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     John Stultz <john.stultz@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     lkml <linux-kernel@...r.kernel.org>, Yu Chen <chenyu56@...wei.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Felipe Balbi <balbi@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Jun Li <lijun.kernel@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Linux USB List <linux-usb@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [RFC][PATCH 2/3] usb: roles: Add usb role switch notifier.

Hi,

On 03-10-2019 22:45, John Stultz wrote:
> On Thu, Oct 3, 2019 at 4:26 AM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
>>
>> On Wed, Oct 02, 2019 at 11:16:16PM +0000, John Stultz wrote:
>>> From: Yu Chen <chenyu56@...wei.com>
>>>
>>> This patch adds notifier for drivers want to be informed of the usb role
>>> switch.
>>
>> Ick, I hate notifiers, they always come back to cause problems.
>>
>> What's just wrong with a "real" call to who ever needs to know this?
>> And who does need to know this anyway?  Like Hans said, if we don't have
>> a user for it, we should not add it.
> 
> So in this case, its used for interactions between the dwc3 driver and
> the hikey960 integrated USB hub, which is controlled via gpio (which I
> didn't submit here as I was trying to keep things short and
> reviewable, but likely misjudged).
> 
> The HiKey960 has only one USB controller, but in order to support both
> USB-C gadget/OTG and USB-A (host only) ports. When the USB-C
> connection is attached, it powers down and disconnects the hub. When
> the USB-C connection is detached, it powers the hub on and connects
> the controller to the hub.

When you say one controller, do you mean 1 host and 1 gadget controller,
or is this one of these lovely devices where a gadget controller gets
abused as / confused with a proper host controller?

And since you are doing a usb-role-switch driver, I guess that the
role-switch is integrated inside the SoC, so you only get one pair
of USB datalines to the outside ?

This does seem rather special, it might help if you can provide a diagram
with both the relevant bits inside the SoC as well as what lives outside
the Soc. even if it is in ASCII art...

Regards,

Hans