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

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Message-ID: <20160822203947.ksxwnvzhc3tpnnx7@earth>
Date:   Mon, 22 Aug 2016 22:39:48 +0200
From:   Sebastian Reichel <sre@...nel.org>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
        Oleksij Rempel <linux@...pel-privat.de>,
        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>, 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,

On Sun, Aug 21, 2016 at 09:50:57AM +0200, H. Nikolaus Schaller wrote:
> > Am 20.08.2016 um 15:34 schrieb One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>:
> >> What it is not about are UART/RS232 converters connected through USB or virtual
> >> serial ports created for WWAN modems (e.g. /dev/ttyACM, /dev/ttyHSO). Or BT devices
> >> connected through USB (even if they also run HCI protocol).
> > 
> > It actually has to be about both because you will find the exact same
> > device wired via USB SSIC/HSIC to a USB UART or via a classic UART. Not is
> > it just about embedded boards. 
> 
> Not necessarily.
> 
> We often have two interface options for exactly the sam sensor chips. They can be connected
> either through SPI or I2C. Which means that there is a core driver for the chip and two different
> transport glue components (see e.g. iio/accel/bmc150).
> 
> This does not require I2C to be able to handle SPI or vice versa or provide a common API.

I don't understand this comparison. I2C and SPI are different
protocols, while native UART and USB-connected UART are both UART.

> And most Bluetooth devices I know have either UART or a direct
> USB interface. So in the USB case there is no need to connect
> it through some USB-UART bridge and treat it as an UART at all.

I think having support for USB-UART dongles is useful for
driver development and testing on non-embedded HW.

-- Sebastian

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