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

Stephen Warren swarren at wwwdotorg.org
Wed Sep 23 08:18:53 PDT 2015

On 09/23/2015 04:01 AM, Martin Sperl wrote:
> On 22.09.2015 04:42, Stephen Warren wrote:
>> On 09/11/2015 05:20 AM, kernel at martin.sperl.org wrote:
>>> From: Martin Sperl <kernel at martin.sperl.org>
>>> 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.
> OK - I will look into creating a separate driver then that uses the 8250
> implementation as a basis...

I expect all you need to do is add a new PORT_* value to the existing 
driver (which then drives some new quirk setting re: the clock rate), 
and add new entry for the compatible value in of_platform_serial_table[] 
in drivers/tty/serial/of_serial.c to select the correct TYPE_*.

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