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

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Date:   Mon, 22 Jul 2019 13:48:39 +0200
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Pawel Laszczak <pawell@...ence.com>
Cc:     Pavel Machek <pavel@....cz>,
        "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, Jul 22, 2019 at 09:58:42AM +0000, Pawel Laszczak 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.

thanks,

greg k-h