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Date:   Thu, 2 Sep 2021 16:35:29 +0200
From:   Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Rob Herring <robh@kernel.org>, linuxarm@huawei.com,
        mauro.chehab@huawei.com, John Stultz <john.stultz@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>, linux-kernel@vger.kernel.org,
        Matthias Kaehlcke <mka@chromium.org>
Subject: Re: [PATCH v3 2/4] misc: hisi_hikey_usb: change the DT schema
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Em Thu, 2 Sep 2021 15:56:36 +0200
Greg Kroah-Hartman <gregkh@linuxfoundation.org> escreveu:

> On Thu, Sep 02, 2021 at 03:38:20PM +0200, Mauro Carvalho Chehab wrote:
> > Em Thu, 2 Sep 2021 15:10:53 +0200
> > Mauro Carvalho Chehab <mchehab+huawei@kernel.org> escreveu:
> >   
> > > Em Thu, 2 Sep 2021 13:40:28 +0200
> > > Greg Kroah-Hartman <gregkh@linuxfoundation.org> escreveu:
> > >   
> > > > On Thu, Sep 02, 2021 at 01:28:35PM +0200, Mauro Carvalho Chehab wrote:    
> > > > > As there's no upstream DT bindings for this driver, let's
> > > > > update its DT schema, while it is not too late.      
> > > > 
> > > > So this is for 5.15-final?    
> > > 
> > > It can either be for 5.15 or 5.16, as there aren't any compatible
> > > under arch/ which uses the DT schema there. All patches adding
> > > such compatible are on this series. So, whatever version this
> > > is applied should be OK.  
> > 
> > On a separate note, despite having "hisi_" on this driver's name, there's
> > nothing there that is really HiSilicon specific. What this driver does is
> > to control an USB HUB integrated inside a DT-based board, doing those 
> > functions:
> > 
> > 	- Power on/off the chip;
> > 	- reset the HUB;
> > 	- control its OTG switch;
> > 	- control power on/off for an USB type-C connector;
> > 	- set USB role as host or device.
> > 
> > This is used on both HiKey 960 and HiKey 970 with the following
> > topology:
> > 
> >   +-----+      +--------+       +---------+
> >   | SoC | ---> | USB PHY|  ---> | USB HUB | ---> USB 3.0
> >   +-----+      +--------+       +---------+      and type-C ports 
> > 
> > Both Kirin 960 and 970 SoCs have a Synapsys IP (DWC 3). 
> > 
> > Both HiKey 960 and 970 cards use Richtek RT1711H Type-C Chip Driver
> > as part of the USB PHY logic, but they use different USB HUBs:
> > 
> > 	- HiKey 960 use a Microchip USB5734 HUB
> > 	- HiKey 970 use a TI TUSB8041 HUB
> > 
> > While I'm not sure how generic this driver can be, I'm thinking that
> > maybe a future patch could rename it to 'generic-usb-hub' or 
> > something similar - finding a good name is always the hardest 
> > part :-)  
> 
> Try looking at:
> 	https://lore.kernel.org/r/20210813195228.2003500-1-mka@chromium.org
> for another example of this.

(C/C Matthias here).

Interesting to know that someone else is also needing to add support
for USB chips.

Yet, the approach took there won't work with HiKey 960/970, as
it needs to control not only the regulator, but it should also
work as as usb-role-switch. 

So, besides controlling the regulator, which seems to be basically what
the onboard_usb_hub_driver does, but it should also be able to:

 	- (optionally) reset the HUB;
	- control its OTG switch;
 	- control power on/off for an USB type-C connector;
 	- set USB role as host or device.

Perhaps it would be possible to merge both approaches by modifying
hisi_hikey_usb in order to add the extra bits required by the boards that
Matthias is currently working, and requiring the GPIOs for OTG and
type-C connectors only if DT contains usb-role-switch.

Thanks,
Mauro