2015-12-23 10:28:39

by Ranjit Waghmode

Subject: [RFC LINUX PATCH] dt: xilinx: xadc: provision to control clock frequency

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

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

Signed-off-by: Ranjit Waghmode <[email protected]>
---
Documentation/devicetree/bindings/iio/adc/xilinx-xadc.txt | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/adc/xilinx-xadc.txt b/Documentation/devicetree/bindings/iio/adc/xilinx-xadc.txt
index d71258e..2cabb9b 100644
--- a/Documentation/devicetree/bindings/iio/adc/xilinx-xadc.txt
+++ b/Documentation/devicetree/bindings/iio/adc/xilinx-xadc.txt
@@ -20,6 +20,11 @@ Required properties:
- clocks: When using the ZYNQ this must be the ZYNQ PCAP clock,
when using the AXI-XADC pcore this must be the clock that provides the
clock to the AXI bus interface of the core.
+ - tck-rate: clock frequency control
+ * 0x0: 1/2 of clock frequency
+ * 0x1: 1/4 of clock frequency
+ * 0x2: 1/8 of clock frequency
+ * 0x3: 1/16 of clock frequency

Optional properties:
- interrupt-parent: phandle to the parent interrupt controller
@@ -79,6 +84,7 @@ Examples:
interrupts = <0 7 4>;
interrupt-parent = <&gic>;
clocks = <&pcap_clk>;
+ tck-rate = <0x3>;

xlnx,channels {
#address-cells = <1>;
@@ -101,6 +107,7 @@ Examples:
interrupts = <0 53 4>;
interrupt-parent = <&gic>;
clocks = <&fpga1_clk>;
+ tck-rate = <0x3>;

xlnx,channels {
#address-cells = <1>;
--
2.1.2

2015-12-23 11:48:10

by Soren Brinkmann

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