linux-kernel - Re: [RFC LINUX PATCH] dt: xilinx: xadc: provision to control clock frequency

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Message-ID: <20151223114908.GG6491@xsjsorenbubuntu>
Date:	Wed, 23 Dec 2015 03:49:08 -0800
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Ranjit Waghmode <ranjit.waghmode@...inx.com>
CC:	<robh+dt@...nel.org>, <pawel.moll@....com>, <mark.rutland@....com>,
	<ijc+devicetree@...lion.org.uk>, <galak@...eaurora.org>,
	<michal.simek@...inx.com>, <corbet@....net>, <lars@...afoo.de>,
	<devicetree@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <punnaia@...inx.com>,
	<anirudh@...inx.com>
Subject: Re: [RFC LINUX PATCH] dt: xilinx: xadc: provision to control clock
 frequency

On Wed, 2015-12-23 at 03:58PM +0530, Ranjit Waghmode wrote:
> This patch adds parameter to the xilinx-xadc node for controlling
> clock frequency.
> 
> Following are the possible options for user to control the frequency:
> 	* 00 : 1/2 of clock frequency
> 	* 01 : 1/4 of clock frequency
> 	* 10 : 1/8 of clock frequency
> 	* 11 : 1/16 of clock frequency

How is this chosen? Are these just arbitrary values that you need for
some use-case? Or are these the options HW allows?

> 
> So this patch adds parameter tck-rate to set user defined values from
> above pool to control the clock frequency.

This is no longer describing HW, but configuring driver/HW. Why does
this have to be in DT? Why can't the driver request/set the frequency as
operation requires it?

	Thanks,
	Sören
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