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

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Date:   Sat, 27 Aug 2016 14:01:54 +0200
From:   Michal Suchanek <hramrach@...il.com>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Sebastian Reichel <sre@...nel.org>,
        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

On 22 August 2016 at 23:23, H. Nikolaus Schaller <hns@...delico.com> wrote:
> Hi Sebastian,
>
>> Am 22.08.2016 um 22:39 schrieb Sebastian Reichel <sre@...nel.org>:
>>
>> 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,
>
> Yes, they are different on protocol level, but on both you transfer blocks of data from/to a slave device
> which usually can be addressed. And for some chips they are just two slightly alternative serial interfaces.
>
>> while native UART and USB-connected UART are both UART.
>
> I see what you mean, but kernel divides between directly connected UART and USB-connected UART.
>
> drivers/usb/serial/ vs. drivers/tty/serial/
>
> to implement two different groups of UARTs. Although on user space level they are harmonized again.
> This is why I compare with i2c and spi. But each such comparison is not perfect.
>
> Anyways, to me it looks as if everybody wants to make the solution work for usb-uarts as well
> (although I still would like to see a real world use-case).

I use a NFC reader attached to a PL2303 UART. It's a proof of concept
solution but if I needed a finished
product all it takes is to put the two pieces of PCB into a box with
the USB connector sticking out.
Or glue the PCB on the inside of a plastic part of a PC case.

Thanks

Michal