linux-kernel - Re: [PATCH RFC] clk: Introduce userspace clock driver

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Message-ID: <0bf5a185-86f7-4a93-a90f-42caefb06a1d@TX2EHSMHS009.ehs.local>
Date:	Mon, 13 May 2013 09:09:47 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Mark Brown <broonie@...nel.org>
CC:	Mike Turquette <mturquette@...aro.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH RFC] clk: Introduce userspace clock driver

On Mon, May 13, 2013 at 09:21:35AM +0400, Mark Brown wrote:
> On Sun, May 12, 2013 at 12:05:04PM -0700, Sören Brinkmann wrote:
> > On Sun, May 12, 2013 at 06:33:44PM +0400, Mark Brown wrote:
> 
> > > No, there's no confusion here - the clocks that are being exposed to
> > > userspace are the clocks which enter the FPGA.  The driver or whatever
> > > that understands the FPGA can do what is needed to control them,
> > > including routing them on to subdevices it instantiates or exposing them
> > > to userspace.
> 
> > Such a driver does not exist in general.
> > For some IP cores, Linux drivers do exist and then
> > they are supposed to directly use the CCF, IMHO, no need to expose
> > things to userspace in that case.
> > I'm trying to cover cases, in which there is no driver available/needed for
> > the FPGA design, other than some simple clock controls.
> 
> You're not understanding the point here.  If you've got a
> reprogrammmable FPGA you at least need some way to get the FPGA image in
> there.  This driver is presumably responsible for instantiating whatever
> is needed to control what is on the FPGA, that could include punting the
> clocks to userspace if that's sane.
Well, that driver actually exists. But that just programs a bitstream
you give it to program. It does not know anything about the design it
programs and cannot make any kind of decision whether the clocks should
be userspace controlled or not.

	Sören


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