linux-kernel - Re: [PATCH v10 2/5] USB: misc: Add onboard_usb

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Message-ID: <20210521011436.GA1224757@rowland.harvard.edu>
Date:   Thu, 20 May 2021 21:14:36 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Michal Simek <michal.simek@...inx.com>,
        devicetree@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        linux-usb@...r.kernel.org, Peter Chen <peter.chen@...nel.org>,
        linux-kernel@...r.kernel.org, Stephen Boyd <swboyd@...omium.org>,
        Ravi Chandra Sadineni <ravisadineni@...omium.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Bastien Nocera <hadess@...ess.net>,
        Al Cooper <alcooperx@...il.com>,
        "Alexander A. Klimov" <grandmaster@...klimov.de>,
        Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH v10 2/5] USB: misc: Add onboard_usb_hub driver

On Thu, May 20, 2021 at 02:14:15PM -0700, Matthias Kaehlcke wrote:
> On Thu, May 20, 2021 at 06:41:23AM -0700, Matthias Kaehlcke wrote:
> > On Wed, May 19, 2021 at 10:05:21PM -0400, Alan Stern wrote:
> > > On Wed, May 19, 2021 at 04:07:17PM -0700, Matthias Kaehlcke wrote:
> > > > On Wed, May 19, 2021 at 10:43:56AM -0400, Alan Stern wrote:
> > > > > On Tue, May 18, 2021 at 02:40:47PM -0700, Matthias Kaehlcke wrote:
> > > > > > 
> > > > > > Could you also have a look at "[4/5] usb: host: xhci-plat:
> > > > > > Create platform device for onboard hubs in probe()"
> > > > > > (https://lore.kernel.org/patchwork/patch/1425453/)? It's a
> > > > > > relatively short patch that creates the platform device for
> > > > > > the driver from xhci-plat as you suggested in the v4
> > > > > > discussion.
> > > > > 
> > > > > I'm not the maintainer for xhci-related drivers.
> > > > > 
> > > > > However, there is at least one thing about this patch which looks 
> > > > > suspicious: Adding the onboard_hub_dev pointer to struct usb_hcd instead 
> > > > > of to struct xhci_plat_priv, where it would make a lot more sense.
> > > > 
> > > > I can move it to struct usb_hcd if that's preferred
> > > 
> > > Thinko: The patch already has it in struct usb_hcd.  I suggested moving 
> > > it to struct xhci_plat_priv.
> > 
> > Ah, didn't actively recall to which struct I added it to, it has been a
> > while since I wrote that patch ;-)
> 
> > Agreed that struct xhci_plat_priv is a better place.
> 
> Or not, xhci_plat_priv is optional, which doesn't make it a good candidate
> for holding a field that could be used by any xHCI controller.

You could always allocate an xhci_plat_priv structure in cases where an 
onboard-hub device is present, if one doesn't exist already.

> Should I move the field to struct xhci_hcd instead?

That's another option.

Look, I'm not the person you should be asking about this.  What I say 
doesn't matter -- you need to get approval from Mathias Nyman, the 
xhci-hcd maintainer.

Alan Stern