Re: [PATCH 10/10] drivers: PL011: add support for the ARM SBSA generic UART

[Andre Przywara <andre.przywara@arm.com>]

Hi,

On 19/01/15 13:31, Arnd Bergmann wrote:
> On Friday 16 January 2015 18:37:17 Mark Rutland wrote:
>>
>>> Makes some sense, so what about:
>>> -----------------------
>>> Required properties:
>>> - compatible: must be "arm,sbsa-uart"
>>> - reg: exactly one register range
>>> - interrupts: exactly one interrupt specifier
>>>
>>> Optional properties:
>>> - current-speed : the current active speed of the UART
>>> - fifo-size : always 32 as per the SBSA specification
>>> - word-size : the number of payload bits per word
>>> - parity : used parity method, can be:
>>>       "n": no parity
>>>       "e": even parity
>>>       "o": odd parity
>>>       "m": always mark (logical 1)
>>>       "s": always space (logical 0)
>>> - stop-bits : the number of stop bits after the payload
>>
>> Generally those look fine, though someone more familiar with serial
>> should take a look.
>>
>> We can drop fifo-size given it's fixed. Anything that we know outright
>> doesn't need to be described.
>>
>> We might want to make them mandatory. I don't see any value in not
>> knowing.
> 
> I think making them optional is useless, so either make them mandatory or
> drop them if we can avoid it. Unfortunately, LCR is not part of SBSA,
> that would let us drop the properties and still report the correct settings.
> 
> Would we be better off documenting that 8-n-1 is the only allowed settting?
> I can't think of a reason why anyone would use something else.

Reading the spec again I see that 8-bit word len is mandated:
"The generic UART uses 8-bit words, equivalent to UARTLCR_H.WLEN == b11."
So given this I guess anything other than (8)n1 is pretty useless and
wouldn't probably be used anyways. This means that we can get rid of the
optional properties altogether and just add "current-speed" to the list
of required ones. I am about to implement this.

Cheers,
Andre.