linux-kernel - Re: [PATCH v5 2/5] Documentation: DT: Add bindings for Spreadtrum SoC Platform

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Date:	Sat, 17 Jan 2015 16:10:32 +0800
From:	Orson Zhai <orsonzhai@...il.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Lyra Zhang <zhang.lyra@...il.com>,
	Chunyan Zhang <chunyan.zhang@...eadtrum.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
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	Leo Yan <leo.yan@...aro.org>
Subject: Re: [PATCH v5 2/5] Documentation: DT: Add bindings for Spreadtrum SoC Platform

On Fri, Jan 16, 2015 at 10:11 PM, Mark Rutland <mark.rutland@....com> wrote:
> On Fri, Jan 16, 2015 at 12:53:16PM +0000, Lyra Zhang wrote:
>> Hi, Mark
>>
>> >> +
>> >> +Required properties:
>> >> +- compatible: must be "sprd,sc9836-uart"
>> >> +- reg: offset and length of the register set for the device
>> >> +- interrupts: exactly one interrupt specifier
>> >> +- clocks: phandles to input clocks.
>> >
>> > The order and relevance of each should be specified. If you have
>> > multiple clocks I would strongly recommend you use clock-names to
>> > distinguish them.
>> >
>>
>> Thank you for the recommendation.
>> but, since we haven't made the clock driver ready, for this initial
>> commit, we just let 4 UARTs share a single fixed 26 MHz clock source.
>> we'll do like you've recommended when we will submit the clock driver
>> in the future.
>
> I'm on about the clock input lines on the UART instance, not the
> providers they come from.
>
> Is there only a single clock input line on each UART? Perhaps multiple
> input lines which are currently fed by the same clock?

________
| 26MHz |-------------------------------------------------
-------------        |                  |
                     |                  |
                _______       ________
               | UART1 |      | UART2 |    .........
               --------------      -------------

the hardware is something like the diagram.

4 Uart modules are all connected to a fixed 26Mhz crystal by power-on default.

There should be a clock-mux between uart and 26Mhz which
could select other clock source such as some pll output.

But as initial commit , we are not ready to describe other inputs by
these muxes.
So  we treat the UART as a simple model with only one fixed-clock input.
And we plan to add the other inputs path back in a not very far future.
Is it appropriate  to do like this?

  Orson


>
> Thanks,
> Mark.
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