Subject: [PATCH 3/4] serial: bcm2835: add auxiliary uart1 to device tree of bcm2835

From: [email-masked] (Stephen Warren)
Date: Mon, 21 Sep 2015 19:42:25 -0700

On 09/11/2015 05:20 AM, kernel at martin.sperl.org wrote:
> From: Martin Sperl <[email-masked]>
> 
> Add the auxiliary uart1 device to the device tree of the bcm2835 SOC.

> diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi

> +		uart1: uart at 7e215040 {
> +			compatible = "ns16550";

compatible should always include a precise HW-specific value; something
like brcm,bcm2835-aux-uart. That way, if we find some other issue that
needs working around on this HW in the future, all DTs will already
contain the compatible value that SW needs in order to trigger that
workaround. That's a generally true statement; i.e. irrespective of
anything else in this series.

I don't believe "ns16550" should be in the compatible value for this
device, since the device cannot be successfully driven by SW that only
knows about a standard 16650 UART. SW must know about the different
divider, and there is no possibility of SW knowing about that before
this series.