linux-kernel - Re: [PATCH v3 1/3] usb: misc: onboard-hub: support multiple power supplies

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Date:   Wed, 21 Jun 2023 18:22:41 +0200
From:   Benjamin Bara <bbara93@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Matthias Kaehlcke <mka@...omium.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Benjamin Bara <benjamin.bara@...data.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v3 1/3] usb: misc: onboard-hub: support multiple power supplies

On Wed, 21 Jun 2023 at 18:07, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Wed, Jun 21, 2023 at 05:58:30PM +0200, Benjamin Bara wrote:
> > From: Benjamin Bara <benjamin.bara@...data.com>
> >
> > As some of the onboard hubs require multiple power supplies, provide the
> > environment to support them.
> >
> > Signed-off-by: Benjamin Bara <benjamin.bara@...data.com>
> > ---
> > v3:
> > - fix nits mentioned in v2
> >
> > v2:
> > - replace (err != 0) with (err)
> > ---
> >  drivers/usb/misc/onboard_usb_hub.c | 39 ++++++++++++++++++++++++++++++--------
> >  drivers/usb/misc/onboard_usb_hub.h |  1 +
> >  2 files changed, 32 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/usb/misc/onboard_usb_hub.c b/drivers/usb/misc/onboard_usb_hub.c
> > index 12fc6eb67c3b..a56e712d3a45 100644
> > --- a/drivers/usb/misc/onboard_usb_hub.c
> > +++ b/drivers/usb/misc/onboard_usb_hub.c
> > @@ -27,6 +27,13 @@
> >
> >  #include "onboard_usb_hub.h"
> >
> > +#define MAX_SUPPLIES 2
>
> Why 2?

I picked 2 because with 3/3, this is the maximum of "required" supplies. The
currently implemented ones require only one (up to now just named "vdd"). The
new one added in 3/3 requires 2, therefore I tried to be generic if some future
hub might require 3 or more.

> > +
> > +static const char * const supply_names[] = {
> > +     "vdd",
> > +     "vdd2",
> > +};
>
> Do those names have anything to do with the number above?  If so, please
> document it!

I picked "vdd" for the first to be compatible with the existing device-trees. As
the actual names differ between hubs, I thought it might be generic to just use
"vdd2" here. If I should add some comment like "if you increase MAX_SUPPLIES,
please also add a supply_name below", I can do that. I could also implement
"vdd${i+1}" for i>0 instead.

>
> >  struct onboard_hub_pdata {
> >       unsigned long reset_us;         /* reset pulse width in us */
> > +     unsigned int num_supplies;      /* number of supplies: 0 considered as 1 */
>
> I can not understand that comment at all :(

This should just indicate that leaving the field empty means one supply is
required. Maybe "defaults to 1" is better?