linux-kernel - Re: [PATCH v2 03/22] usb: dwc3: glue: Allow more fine grained control over mode switches

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Message-ID: <20250924224912.riddb2chjqrdi2xj@synopsys.com>
Date: Wed, 24 Sep 2025 22:49:16 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Sven Peter <sven@...nel.org>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, Felipe Balbi <balbi@...nel.org>,
        Janne Grunau <j@...nau.net>, Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Neal Gompa <neal@...pa.dev>, Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Philipp Zabel <p.zabel@...gutronix.de>, Frank Li <Frank.Li@....com>,
        Ran Wang <ran.wang_1@....com>, Peter Chen <peter.chen@....com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "asahi@...ts.linux.dev" <asahi@...ts.linux.dev>,
        "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
        "linux-phy@...ts.infradead.org" <linux-phy@...ts.infradead.org>
Subject: Re: [PATCH v2 03/22] usb: dwc3: glue: Allow more fine grained control
 over mode switches

On Sat, Sep 20, 2025, Sven Peter wrote:
> Hi,
> 
> On 19.09.25 23:40, Thinh Nguyen wrote:
> > On Sat, Sep 06, 2025, Sven Peter wrote:
> > > We need fine grained control over mode switched on the DWC3 controller
> > > present on Apple Silicon. Export core, host and gadget init and exit,
> > > ptrcap and susphy control functions. Also introduce an additional
> > > parameter to probe_data that allows to skip the final initialization
> > > step that would bring up host or gadget mode.
> > > 
> > > Signed-off-by: Sven Peter <sven@...nel.org>
> > > ---
> > >   drivers/usb/dwc3/core.c   | 16 +++++++++++-----
> > >   drivers/usb/dwc3/gadget.c |  2 ++
> > >   drivers/usb/dwc3/glue.h   | 14 ++++++++++++++
> > >   drivers/usb/dwc3/host.c   |  2 ++
> > >   4 files changed, 29 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> > > index 8002c23a5a02acb8f3e87b2662a53998a4cf4f5c..18056fac44c8732278a650ac2be8b493892c92dd 100644
> > > --- a/drivers/usb/dwc3/core.c
> > > +++ b/drivers/usb/dwc3/core.c
> > > @@ -132,6 +132,7 @@ void dwc3_enable_susphy(struct dwc3 *dwc, bool enable)
> > >   		dwc3_writel(dwc->regs, DWC3_GUSB2PHYCFG(i), reg);
> > >   	}
> > >   }
> > > +EXPORT_SYMBOL_GPL(dwc3_enable_susphy);
> > >   void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode, bool ignore_susphy)
> > >   {
> > > @@ -157,6 +158,7 @@ void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode, bool ignore_susphy)
> > >   	dwc->current_dr_role = mode;
> > >   }
> > > +EXPORT_SYMBOL_GPL(dwc3_set_prtcap);
> > 
> > I'm hesitant to export this as is. This function may change the susphy
> > bits and expect them to be restored later. It's not meant to be a
> > standalone use. At least, we should document how it should be used along
> > with the other newly added interfaces.
> 
> 
> Sure, I can otherwise also open-code the susphy change inside
> dwc3_apple_phy_set_mode anyway if you prefer to keep this private to the
> dwc3 core. I should restore it there to the original value anyway I guess
> after phy_set_mode.
> 

I think if you can help document how to use dwc3_set_prtcap(), it will
be fine.

> 
> 
> > >   static void __dwc3_set_mode(struct work_struct *work)
> 
> [...]
> 
> > >   int dwc3_gadget_suspend(struct dwc3 *dwc)
> > >   {
> > > diff --git a/drivers/usb/dwc3/glue.h b/drivers/usb/dwc3/glue.h
> > > index 2efd00e763be4fc51911f32d43054059e61fb43a..633268c76fe4c7fdc312c9705dfa7cf7ccf3544c 100644
> > > --- a/drivers/usb/dwc3/glue.h
> > > +++ b/drivers/usb/dwc3/glue.h
> > > @@ -15,16 +15,30 @@
> > >    * @res: resource for the DWC3 core mmio region
> > >    * @ignore_clocks_and_resets: clocks and resets defined for the device should
> > >    *		be ignored by the DWC3 core, as they are managed by the glue
> > > + * @skip_core_init_mode: skip the finial initialization of the target mode, as
> > 
> > finial -> final?
> 
> Whoops, yes, I thought I ran a spell checker over this because I usually add
> a lot of typos but must've forgotten :-)
> 
> 
> > 
> > > + *		it must be managed by the glue
> > >    */
> 
> [...]
> 
> > > +int dwc3_core_init(struct dwc3 *dwc);
> > > +void dwc3_core_exit(struct dwc3 *dwc);
> > > +
> > > +int dwc3_host_init(struct dwc3 *dwc);
> > > +void dwc3_host_exit(struct dwc3 *dwc);
> > > +int dwc3_gadget_init(struct dwc3 *dwc);
> > > +void dwc3_gadget_exit(struct dwc3 *dwc);
> > > +
> > > +void dwc3_enable_susphy(struct dwc3 *dwc, bool enable);
> > > +void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode, bool ignore_susphy);
> > > +
> > 
> > We should document these interfaces. The dwc3_core_probe() does all of
> > the above in the proper order. It's not obvious why these are needed and
> > how they should be used.
> 
> Very good point, I'll add documentation for all of these!
> 
> 

Thanks Sven!
Thinh