linux-kernel - Re: [PATCH v10 0/6] Introduced new Cadence USBSS DRD Driver.

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Message-ID: <20190722210021.GA25235@amd>
Date:   Mon, 22 Jul 2019 23:00:21 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Pavel Machek <pavel@...x.de>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Pawel Laszczak <pawell@...ence.com>,
        "felipe.balbi@...ux.intel.com" <felipe.balbi@...ux.intel.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "rogerq@...com" <rogerq@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jbergsagel@...com" <jbergsagel@...com>,
        "nsekhar@...com" <nsekhar@...com>, "nm@...com" <nm@...com>,
        Suresh Punnoose <sureshp@...ence.com>,
        Jayshri Dajiram Pawar <jpawar@...ence.com>,
        Rahul Kumar <kurahul@...ence.com>,
        Anil Joy Varughese <aniljoy@...ence.com>
Subject: Re: [PATCH v10 0/6] Introduced new Cadence USBSS DRD Driver.

On Mon 2019-07-22 13:56:44, Pavel Machek wrote:
> Hi!
> 
> > > >> This patch introduce new Cadence USBSS DRD driver to linux kernel.
> > > >>
> > > >> The Cadence USBSS DRD Controller is a highly configurable IP Core which
> > > >> can be instantiated as Dual-Role Device (DRD), Peripheral Only and
> > > >> Host Only (XHCI)configurations.
> > > >
> > > >I see you are using debugfs to select between DRD, peripheral-onlyh and XHCI...
> > > >
> > > >Is that good idea?
> > > 
> > > Yes driver allows selecting dr_mode by debugfs. Controller also support such functionality 
> > > so I don't understand why would it not be a good idea. 
> > > 
> > > I personally use this for testing but it can be used to limit controller functionality without 
> > > recompiling kernel. 
> > 
> > debugfs is ONLY for debugging, never rely on it being enabled, or
> > mounted, on a system in order to have any normal operation happen.
> > 
> > So for testing, yes, this is fine.  If this is going to be the normal
> > api/interface for how to control this driver, no, that is not acceptable
> > at all.
> 
> It makes a lot of sense for end-user to toggle this... for example
> when he is lacking right cable for proper otg detection. As it is
> third driver offering this functionality, I believe we should stop
> treating it as debugging.

At least renesas usb controller seems to have variables in sysfs:
drivers/phy/renesas/phy-rcar-gen3-usb2.c : functions role_show and
role_store. See also
Documentation/ABI/testing/sysfs-platform-phy-rcar-gen3-usb2 .

I believe this driver should do same.

Thanks and best regards,
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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