linux-kernel - Re: [PATCH 4/4] USB: gadget: Add a new bus for gadgets

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Message-ID: <CAMuHMdUpOiHHMktPk_-NauDW2ufvGThnkFU7Pok376pM6OEyYw@mail.gmail.com>
Date:   Mon, 9 May 2022 09:46:25 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        USB mailing list <linux-usb@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
Subject: Re: [PATCH 4/4] USB: gadget: Add a new bus for gadgets

Hi Alan,

On Sat, May 7, 2022 at 5:36 PM Alan Stern <stern@...land.harvard.edu> wrote:
> On Tue, May 03, 2022 at 11:48:33AM -0400, Alan Stern wrote:
> > On Tue, May 03, 2022 at 05:27:08PM +0200, Geert Uytterhoeven wrote:
> > > On Tue, May 3, 2022 at 5:14 PM Alan Stern <stern@...land.harvard.edu> wrote:
> > > > On Tue, May 03, 2022 at 12:14:30PM +0200, Geert Uytterhoeven wrote:
> > > > > On Sat, 23 Apr 2022, Alan Stern wrote:
> > > > > > This patch adds a "gadget" bus and uses it for registering gadgets and
> > > > > > their drivers.  From now on, bindings will be managed by the driver
> > > > > > core rather than through ad-hoc manipulations in the UDC core.
> > > > > >
> > > > > > As part of this change, the driver_pending_list is removed.  The UDC
> > > > > > core won't need to keep track of unbound drivers for later binding,
> > > > > > because the driver core handles all of that for us.
> > > > > >
> > > > > > However, we do need one new feature: a way to prevent gadget drivers
> > > > > > from being bound to more than one gadget at a time.  The existing code
> > > > > > does this automatically, but the driver core doesn't -- it's perfectly
> > > > > > happy to bind a single driver to all the matching devices on the bus.
> > > > > > The patch adds a new bitflag to the usb_gadget_driver structure for
> > > > > > this purpose.
> > > > > >
> > > > > > A nice side effect of this change is a reduction in the total lines of
> > > > > > code, since now the driver core will do part of the work that the UDC
> > > > > > used to do.
> > > > > >
> > > > > > A possible future patch could add udc devices to the gadget bus, say
> > > > > > as a separate device type.
> > > > > >
> > > > > > Signed-off-by: Alan Stern <stern@...land.harvard.edu>
> > > > >
> > > > > Thanks for your patch, which is now commit fc274c1e997314bf ("USB:
> > > > > gadget: Add a new bus for gadgets") in usb-next.
> > > > >
> > > > > This patch cause a regression on the Renesas Salvator-XS development
> > > > > board, as R-Car H3 has multiple USB gadget devices:
> > > >
> > > > Then these gadgets ought to have distinct names in order to avoid the
> > > > conflict below:
>
> Geert:
>
> Can you test the patch below?  It ought to fix the problem (although it

Thanks!

root@...salvator-xs:~# ls -l /sys/bus/gadget/devices/
total 0
lrwxrwxrwx 1 root root 0 Feb 14  2019 gadget.0 ->
../../../devices/platform/soc/e659c000.usb/gadget.0
lrwxrwxrwx 1 root root 0 Feb 14  2019 gadget.1 ->
../../../devices/platform/soc/ee020000.usb/gadget.1
lrwxrwxrwx 1 root root 0 Feb 14  2019 gadget.2 ->
../../../devices/platform/soc/e6590000.usb/gadget.2

Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>

LGTM, so
Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>

> might end up causing other problems down the line...)

Can you please elaborate? I'm not too familiar with UBS gadgets.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds