Re: 8250-based SoC serial ports and features

[Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>]

On Saturday 25 April 2015 16:33:18 Joachim Eastwood wrote:
> 
> One other question: What is the preferred way of describing different
> UART SoC features in DT?
> 16550a is used as base on most NXP Cortex-M devices, but each UART can
> have different features like; IRDA, Smart card, RS485, sync mode
> (USART), DMA, hardware RTS/CTS pins and full modem pins.
> Features also differ between UARTs on the same device.
> 
> I am thinking about either using different comp strings or some kind
> of feature flags in DT. (Freescale UART already uses feature flags
> like: "fsl,irda-mode" and "fsl,uart-has-rtscts")

I would probably specify both then, to give more flexibility to the
driver in implementing it one way or the other.

> All UARTs on LPC1850 have RS485 and DMA support. In additional you have:
> UART0,2,3: sync mode and smart card.
> UART3: IRDA
> UART1: full modem control pin set.
> 
> Comp strings could be something like:
> "nxp,lpc1850-usart" <- sync+smart card
> "nxp,lpc1850-usart-irda" <- sync+smart card+irda
> "nxp,lpc1850-uart-modem" <- modem-pins
> 
> or feature flags like:
> nxp,sync-mode;
> nxp,rs485-mode;
> nxp,smart-card;
> nxp,irda-mode;
> nxp,full-modem;

For cases where a single chip has uarts with different features,
using feature flags makes most sense, you can probably skip
assigning different compatible strings there.

	Arnd
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