On Monday 18 April 2016 14:34:12 Geert Uytterhoeven wrote: > Hi Arnd, > > CC Richard (serial-mctrl-gpio) > CC Grant (ePAPR successor) and Frank > > On Sat, Apr 16, 2016 at 6:30 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Thursday 14 April 2016 14:13:19 Geert Uytterhoeven wrote: > >> Document a set of generic properties for describing UARTs in a > >> device tree: > >> 1. The GPIO modem control properties are currently duplicated across > >> hardware-specific binding documentation, > >> 2. The property for dedicated RTS/CTS hardware flow control lines is > >> already supported by several drivers, albeit with a vendor-specific > >> prefix, hence make it generic. > >> > >> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx> > > > > Originally the ISA 8250 uart binding (from ieee) was used as the > > template for other uart bindings. How about documenting the parts that > > are used in 8250-of today (current-speed, clock-frequency, > > reg-offset, reg-shift, fifo-size, reg-io-width, auto-flow-control) > > in the same file? > > I don't think we have the habit of documenting (duplicating) bindings for ePAPR > under Documentation/devicetree/bindings/. Perhaps we should? > > Apart from that, most of the properties you mention look legacy or overly > broad too me. > > - current-speed: This is configuration, not a property of the hardware. > For the console, this has been deprecated by appending the serial config > to chosen/stdout-path (e.g. "serial0:115200n8"). > For non-consoles, its use is debatable, IMHO. > It's users are mostly legacy powerpc and early adaptors of DT on ARM. > - clock-frequency: Legacy predating the Common Clock Framework. > Any modern SoC uses clock specifiers with clock handles pointing to clock > providers. I think both are still used by IBM Firmware, which does not use the clock binding or the linux syntax for passing the speed. > - reg-offset, reg-shift, reg-io-width: These are much broader than serial, > and IMHO thus don't belong in > Documentation/devicetree/bindings/serial/serial.txt. The exact meaning can be explained elsewhere, but I think the binding can mention that they are allowed. > - auto-flow-control: Looks a bit like a vague version of "uart-has-rtscts". > Documentation/devicetree/bindings/serial/8250.txt doesn't make it clear > whether this is about hardware capabilities or software configuration. > Even the driver doesn't make it clear: > #define UART_CAP_AFE (1 << 11) /* MCR-based hw flow control */ > "MCR" could mean RTS/CTS, DSR/DTR, ... > - fifo-size: This one could be generic. atmel-usart uses a vendor-specific > version "atmel,fifo-size". > > I suggest we move forward with my initial set, as I have patches that depend on > them? We can always add more properties later. Sounds ok to me. > >> - out1-gpios: Must contain a GPIO specifier, referring to the GPIO pin to be > >> used as the UART's OUT1 line. > >> - out2-gpios: Must contain a GPIO specifier, referring to the GPIO pin to be > >> used as the UART's OUT2 line. > > > > I had to look up what OUT1 and OUT2 are, but I still don't see how you'd > > implement them using a GPIO line: From all I can tell, these are usually > > internal registers in a hardware uart but they are not assigned to an > > external line on the standard db9 or even the old db25 connectors. Should > > we drop these instead? > > They're indeed fairly exotic, and they're burried deeply in the ns16550 > datasheet. We do have TIOCM_OUT1 and TIOCM_LOOP in asm-generic/termios.h, > probably for obscure historical reasons. > > If we drop them, I guess they should be removed from the helper code in > drivers/tty/serial/serial_mctrl_gpio.c, too? There don't seem to be any > current users. I think it makes sense for user space to toggle at least TIOCM_OUT1 through the ioctl and for drivers to implement it correctly. Apparently the "Hayes SmartModem" used this for resetting the modem from its integrated uart. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
