linux-kernel - Re: [RFC PATCH 0/3] UART slave device bus

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Message-ID: <20160822235758.gh33xupgyroye5wa@earth>
Date:   Tue, 23 Aug 2016 01:57:59 +0200
From:   Sebastian Reichel <sre@...nel.org>
To:     One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:     Pavel Machek <pavel@....cz>, Marcel Holtmann <marcel@...tmann.org>,
        Rob Herring <robh@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Peter Hurley <peter@...leysoftware.com>,
        NeilBrown <neil@...wn.name>,
        "Dr . H . Nikolaus Schaller" <hns@...delico.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        "open list:BLUETOOTH DRIVERS" <linux-bluetooth@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/3] UART slave device bus

Hi,

On Mon, Aug 22, 2016 at 11:54:14PM +0100, One Thousand Gnomes wrote:
> On Tue, 23 Aug 2016 00:00:17 +0200
> Pavel Machek <pavel@....cz> wrote:
> 
> > On Mon 2016-08-22 22:32:23, One Thousand Gnomes wrote:
> > > > why would we even have it create a /dev/ttyX for these devices in the first place. Lets just not create an uevent for it and lets not create a dev_t for it.  
> > > 
> > > Because if you don't it's a regression. It's not permissible to break
> > > existing userspace.  
> > 
> > Well... it would be good to do the right thing, at least in the places
> > where we can.
> > 
> > Yes, renumbering people's serials is bad, OTOH for new platforms it
> > would be nice not to expose ttyS15 which can only return -EBUSY.
> 
> That would still be a regression. Not everyone even uses the kernel
> bluetooth stack. It would only return EBUSY if you had done an "up"
> on it via the direct bluetooth stack.

So it returns EBUSY when uart-bus is used. Since uart-bus is about
hardwired devices that's basically always.

Also I wonder how relevant your "I want to handle all UART stuff out of
kernel" scenario is for uart-bus, which is about in-kernel UART
drivers.

-- Sebastian

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