linux-kernel - Re: [PATCH v7 1/5] usb: phy: add usb phy notify port status API

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Date:   Mon, 24 Jul 2023 09:06:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Stanley Chang[昌育德] 
        <stanley_chang@...ltek.com>
Cc:     Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Roy Luo <royluo@...gle.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Flavio Suligoi <f.suligoi@...m.it>,
        Ray Chi <raychi@...gle.com>,
        "linux-phy@...ts.infradead.org" <linux-phy@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH v7 1/5] usb: phy: add usb phy notify port status API

On Mon, Jul 24, 2023 at 06:49:50AM +0000, Stanley Chang[昌育德] wrote:
> 
> > 
> > On Fri, Jul 07, 2023 at 02:47:00PM +0800, Stanley Chang wrote:
> > > In Realtek SoC, the parameter of usb phy is designed to can dynamic
> > > tuning base on port status. Therefore, add a notify callback of phy
> > > driver when usb port status change.
> > >
> > > The Realtek phy driver is designed to dynamically adjust disconnection
> > > level and calibrate phy parameters. When the device connected bit
> > > changes and when the disconnected bit changes, do port status change
> > notification:
> > >
> > > Check if portstatus is USB_PORT_STAT_CONNECTION and portchange is
> > > USB_PORT_STAT_C_CONNECTION.
> > > 1. The device is connected, the driver lowers the disconnection level and
> > >    calibrates the phy parameters.
> > > 2. The device disconnects, the driver increases the disconnect level and
> > >    calibrates the phy parameters.
> > >
> > > When controller to notify connect that device is already ready. If we
> > > adjust the disconnection level in notify_connect, the disconnect may
> > > have been triggered at this stage. So we need to change that as early
> > > as possible. Therefore, we add an api to notify phy the port status changes.
> > 
> > How do you know that the disconnect will not have already been triggered at
> > this point, when the status changes?
> 
> The status change of connection is before port reset.
> In this stage, the device is not port enable, and it will not trigger disconnection.

Ok, then say that here please :)

> > >
> > > Signed-off-by: Stanley Chang <stanley_chang@...ltek.com>
> > > ---
> > > v6 to v7 change:
> > >     No change
> > > v5 to v6 change:
> > >     No change
> > > v4 to v5 change:
> > >     No change
> > > v3 to v4 change:
> > >     Fix the warning for checkpatch with strict.
> > > v2 to v3 change:
> > >     Add more comments about the reason for adding this api
> > > v1 to v2 change:
> > >     No change
> > > ---
> > >  drivers/usb/core/hub.c  | 13 +++++++++++++  include/linux/usb/phy.h |
> > > 13 +++++++++++++
> > >  2 files changed, 26 insertions(+)
> > >
> > > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c index
> > > a739403a9e45..8433ff89dea6 100644
> > > --- a/drivers/usb/core/hub.c
> > > +++ b/drivers/usb/core/hub.c
> > > @@ -614,6 +614,19 @@ static int hub_ext_port_status(struct usb_hub *hub,
> > int port1, int type,
> > >               ret = 0;
> > >       }
> > >       mutex_unlock(&hub->status_mutex);
> > > +
> > > +     if (!ret) {
> > > +             struct usb_device *hdev = hub->hdev;
> > > +
> > > +             if (hdev && !hdev->parent) {
> > 
> > Why the check for no parent?  Please document that here in a comment.
> 
> I will add a comment :
> /* Only notify roothub. That is, when hdev->parent is empty. */

Also document this that this will only happen for root hub status
changes, that's not obvious in the callback name or documentation or
anywhere else here.

> > > +                     struct usb_hcd *hcd = bus_to_hcd(hdev->bus);
> > > +
> > > +                     if (hcd->usb_phy)
> > > +
> > usb_phy_notify_port_status(hcd->usb_phy,
> > > +                                                        port1 -
> > 1, *status, *change);
> > > +             }
> > > +     }
> > > +
> > 
> > This is safe to notify with the hub mutex unlocked?  Again, a comment would
> > be helpful to future people explaining why that is so.
> > 
> 
> I will add a comment: 
> /*                                                                      
>  * There is no need to lock status_mutex here, because status_mutex     
>  * protects hub->status, and the phy driver only checks the port        
>  * status without changing the status.                                  
>  */  

Looks good, if you do it without the trailing whitespace :)

thanks,

greg k-h