Hi, On Mon, Aug 22, 2016 at 11:23:26PM +0200, H. Nikolaus Schaller wrote: > > Am 22.08.2016 um 22:39 schrieb Sebastian Reichel <sre@xxxxxxxxxx>: > > > > 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@xxxxxxxxxxxxxxxxxxx>: > >>>> 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). > > > > >> 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. > > Hm. I assume you mean the Bluetooth situation where both, embedded UART > connected chips and USB dongles are available. No. I mean I have some serial device, which is connected to the embedded UART, but I also have a standalone version. For driver development I can just use my standalone serial device, connect it to an USB-UART and develop the driver on non embedded HW. Then I can use the same driver on my embedded platform and it works, since it uses the same API. For e.g. I2C this works perfectly fine. I already did this with the I2C interface exposed on my notebook's VGA port. > I am not a specialist for such things, but I think you have three > options to connect bluetooth: > > a) SoC-UART <-> BT-Chip-UART-port > b) USB-UART (FT232, PL2303 etc.) <-> BT-Chip-UART-port > c) USB <-> BT-Chip-USB-port (not UART involved at all) > > Case c) IMHO means you anyways need a special USB driver for the BT-Chip connected > through USB and plugging it into a non-embedded USB port does not automatically > show it as a tty interface. So you can't use it for testing the UART drivers. > > BTW: the Wi2Wi W2CBW003 chip comes in two firmware variants: one for UART and > one for USB. So they are also not exchangeable. Yes, let's ignore option c). I'm talking about UART only. If the chip has native USB support, then that's a different driver. Note, that for more complex drivers it may become possible to use the same high-level driver via regmap at some point. Not sure if this kind of HW exists, though. > Variant b) is IMHO of no practical relevance (but I may be wrong) > because it would mean to add some costly FT232 or PL2302 chip > where a different firmware variant works with direct USB > connection. Well for some chips there is not native USB support. But my scenario was about development. Let's say I have a serial-chip and I want to develop a driver for it. It would be nice if I can develop the driver with a USB-UART and then use it on my embedded system. There are usb-serial devices, which could benefit from support btw. I would find it really useful, if the Dangerous Prototype's Bus Pirate would expose native /dev/i2c and /dev/spi and it's based on FT232. > So to me it looks as if you need to develop different low-level > drivers anyways. No. You say, that option b) is irrelevant and assume, that every serial chip also has native USB support. -- Sebastian
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