Re: [PATCH RFC] clk: Introduce userspace clock driver

[Sebastian Hesselbarth]

On 05/13/13 18:09, SÃren Brinkmann wrote:
> On Mon, May 13, 2013 at 09:21:35AM +0400, Mark Brown wrote:
> > On Sun, May 12, 2013 at 12:05:04PM -0700, SÃren 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.

Soeren,

what Mark wants to point out is that you add fabric clocks to the Xilinx
driver instead. This way, you will have user-space controllable clocks
but only if you loaded the xilinx driver first.

IIRC the fabric clock controller provided by Zynq _is_ always there and
accessible from ARM CPUs. You just don't have a new generic driver
allowing to poke with all clocks, but a xilinx only driver allowing you
to set the (xilinx only) fabric clocks.

I've played with Zynq a while ago, did Xilinx mainline the bitfile
driver already? If not, why don't you give it a shot?

Sebastian
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