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

From: Sebastian Hesselbarth
Date: Mon May 13 2013 - 12:21:25 EST


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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