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

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Message-ID: <20160819144428.akddnwfl5g5qhtq3@earth>
Date:   Fri, 19 Aug 2016 16:44:29 +0200
From:   Sebastian Reichel <sre@...nel.org>
To:     One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:     Rob Herring <robh@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Jiri Slaby <jslaby@...e.com>, Pavel Machek <pavel@....cz>,
        Peter Hurley <peter@...leysoftware.com>,
        NeilBrown <neil@...wn.name>,
        "Dr . H . Nikolaus Schaller" <hns@...delico.com>,
        Arnd Bergmann <arnd@...db.de>,
        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 Alan,

On Fri, Aug 19, 2016 at 12:03:05PM +0100, One Thousand Gnomes wrote:
> > I meant "Either some function similar to userspace's poll() is
> > needed, ...". Something like uart_dev_wait_for_rx()
> 
> You can't really do that - it might never return and then how do
> you want to handle timeouts and cleanups

Well there could be some timeout. As I said, I was thinking about
an API similar to poll(), but I agree, that a callback based API
is probably the better solution. It's simpler to implement and in
most cases simpler to use.

> > Alternatively the rx function could be a callback, that
> > is called when there is new data.
> 
> That's what the existing API gives you as an ldisc, it can't be
> immediate in many cases however but must be buffered.

I know and I think the ldisc API is fine in this regard. Also
the buffering allows DMA, so that's obviously preferred.

> > > I'm assuming the only immediate consumers are in-kernel.  
> > 
> > Yes, but the driver should be notified about incoming data.

-- Sebastian

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