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

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Date:   Fri, 26 Aug 2016 14:12:23 +0100
From:   One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:     Rob Herring <robh@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Jiri Slaby <jslaby@...e.com>,
        Sebastian Reichel <sre@...nel.org>,
        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

> Either we'd have to call tty_port->rx a character at a time or
> implement some temporary buffer. I don't think we want to call things
> like BT receive code a byte at a time. This needs to be a layer
> higher. flush_to_ldisc either needs to be duplicated to handle
> tty_port->rx or generalized to call either tty_port->rx or ldisc
> receive_buf. I'm not sure what to do about ldisc ref counting in the
> latter case.

You already have the buffer

What I was trying to suggest was that instead of


chars->buffer
flush
workqueue
loop pushing data into the ldisc


You can also do

chars->buffer
flush
workqueue
->rx()  [where flush_to_ldisc is just one implementation of ->rx]

For byte by byte ports it really makes no difference (except you would be
able to do processing without an ldisc), but for DMA devices it would
give us a faster path for processing since the DMA completion event can
simply fire a buffer a characters directly at the protocol handler where
there are not latency concerns (ie it starts the new DMA and directly
involves ->rx())

Alan