On Tue, Nov 07, 2017 at 08:53:36AM +0100, Michal Oleszczyk wrote: > From: Michal Oleszczyk <oleszczyk.m@xxxxxxxxx> > > Add description of rs485-rts-active-high property into > /serial/rs485.txt devicetree documentation file. Most rs485 transceivers on the market have an active-high Transmit Enable pin, e.g. MAX13451E, SN65HVD1781A: https://datasheets.maximintegrated.com/en/ds/MAX13450E-MAX13451E.pdf http://www.ti.com/lit/gpn/sn65hvd1781a-q1 In fact I'm not aware of a single transceiver that uses active-low, do you know one? I know that omap-serial defaults to active-low and supports an (as yet undocumented) "rs485-rts-active-high" property. I don't know why it defaults to active-low. Adding Mark Jackson to cc who introduced that feature with commit 4a0ac0f55. All other drivers (e.g. imx.c, fsl-lpuart.c) default to active-high. (Which in a way contradicts with your patch as it suggests *everything* defaults to active-low.) I have a series in preparation that I was going to post shortly which instead introduces an rs485-rts-active-low property for those presumably rare cases when it's needed, but retains the current behaviour of omap-serial for compatibility: https://github.com/l1k/linux/commit/03ef500e98e5 https://github.com/l1k/linux/commit/8430ffdb5799 https://github.com/l1k/linux/commit/c3a86d3b862b In my opinion that's a better approach but I'd be curious to hear other opinions. Thanks, Lukas > > Signed-off-by: Michal Oleszczyk <oleszczyk.m@xxxxxxxxx> > --- > Repair 'From' to match with 'Signed-off-by' section. > > Documentation/devicetree/bindings/serial/rs485.txt | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/Documentation/devicetree/bindings/serial/rs485.txt b/Documentation/devicetree/bindings/serial/rs485.txt > index b8415936dfdb..71c38ef7f6e2 100644 > --- a/Documentation/devicetree/bindings/serial/rs485.txt > +++ b/Documentation/devicetree/bindings/serial/rs485.txt > @@ -16,6 +16,8 @@ Optional properties: > feature at boot time. It can be disabled later with proper ioctl. > - rs485-rx-during-tx: empty property that enables the receiving of data even > whilst sending data. > +- rs485-rts-active-high: empty property telling to set RTS line high when it is > + active. > > RS485 example for Atmel USART: > usart0: serial@fff8c000 { -- 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
