AM623: General purpose clock output under Linux

Hi Lyndon,

Please refer to this other thread: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1175479/processor-sdk-am62x-output-audio_ext_refclk0-as-mclk-for-codec-and-mcbsp/4436910?tisearch=e2e-sitesearch&keymatch=AUDIO_EXT_REFCLK#4436910

Where I was able to answer the query similar to what you are asking.

Let me know if this helps. Don't hesitate to contact for further assistance.

Best Regards

Suren

Hi, I have seen this thread before. But I don't see how you use the Clock Tree tool to generate a device tree? It looks like the file "untitled.syscfg" contains C Code. There must be a way for the devie tree to describe the clocking?

I managed to get a 24MHz (960 divide by 40) out of the device, but I had to resort to writing a C code to poke the registers. How can it be achieved via device tree?

// Make MAIN_PLL1_HSDIV6_CLKOUT as a divide by 40 from 960MHz
0x00681098 = 0x00008027
// Enable output and select source as MAIN_PLL1_HSDIV6_CLKOUT)
0x001082E0 = 0x00008006

Hi Lyndon,

I am assigning your query to CTT experts. They should be able to guide you further.

Thanks

Regards

Suren

Lyndon

The current release of the Clock Tree Tool does not support code generation. 

The untitled.sysconfig is the tool configuration save file. 

  Paul 

So is there any way to get a clock out of the AM623 without having to write some sort of clock tree driver? It sounds like there is no device tree support for them? Maybe if I knew what driver/module is responsible for setting up the clocks and PLL - so I can provide some patch to write to these additional register? 

Hi Lyndon,

I'd just directly edit the DTS file of the respective TI board related DTS file (https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/arch/arm64/boot/dts/ti/k3-am62x-sk-common.dtsi?h=ti-rt-linux-5.10.y) your development is based off by copying and pasting items over from the devicetree.dtsi file from the SYSCONFIG tool.

Primarily it would be system-clock-frequency/clock-frequency that points to MCLK in the DTS file.

Also in devicetree.dtsi, pinmux control when selecting AUDIO_EXT_REFCLK would get updated, that you need to copy it in DTS file of the board.

Hope this helps.

Best Regards

Suren

Thanks, I understand that but that doesn't answer the question. Where is the code that is setting up the clocks on this processor?

Hi Lyndon,

In device tree file you can specify the clock frequency of a device. For example in the AM62x DTS file that I shared in my last reply

sound_master: simple-audio-card,codec {
			sound-dai = <&tlv320aic3106>;
			clocks = <&tlv320_mclk>;
		};

tlv320_mclk: clk-0 {
		#clock-cells = <0>;
		compatible = "fixed-clock";
		clock-frequency = <12288000>;
	};

So in the kernel, it is as easy for a driver to use api "of_get_property" to get any data out of device tree.

Please refer the device tree clock binding documentation:

https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/Documentation/devicetree/bindings/clock/clock-bindings.txt?h=ti-rt-linux-5.10.y

Also you can refer more on common clock framework:
https://elinux.org/images/f/f1/Elce2013-clement-common-clock-framework-how-to-use-it.pdf

Hope this clarifies your query on how clocks are set using devicetree.

Best Regards
Suren

Hi,

I am using the k3-am62x-sk-common.dtsi that comes with the SDK and that already has those lines in that you write about. It does not output a clock, which is the same issue the previous thread talks about.

I think that the clock needs setting up in the /arch/arm/mach-k3/am62ax/clk-data.c from U-Boot source, but it says that is an auto generated code:

* AM62AX specific clock platform data
*
* This file is auto generated. Please do not hand edit and report any issues
* to Bryan Brattlof <bb@ti.com>.

Can PaulM answer this question? 

Thanks

Hi Lyndon,

Have you tried to use the k3conf utility to dump clocks on the system and enable required clocks and set them with required frequency.

This utility is already packaged in the Linux SDK release. For more information you could just type k3conf --help. Here are few clock related functions that might be of use.

k3conf dump clock
Prints clock status all the available TISCI clocks

k3conf dump clock <dev_id>
Prints the available clock status for corresponding device id

k3conf enable clock <dev_id> <clk_id>
Enables the TISCI clock and prints the status

k3conf disable clock <dev_id> <clk_id>
Disables the TISCI clock and prints the status

k3conf set clock <dev_id> <clk_id> <freq>
Sets the clock frequency and prints the status

k3conf set parent_clock <dev_id> <clk_id> <parent_clk_id>
Sets the parent clock for a clock mux and prints the mux status
Refer to the following documentation for preconditions:
downloads.ti.com/.../clocks.html
downloads.ti.com/.../clocks.html

Hope this helps.

Best Regards

Suren

Hi,

So If I do:

k3conf set clock 157 7 24000000

There is no clock coming out. I can't find any k3conf command to get the mux in 0x001082E0 set. However, If I do:

k3conf write 0x001082E0 0x00008006

Then it works. But this still begs the question - how should this be added to something like the device tree or set permantly to be done on startup. Is this clock setup done via u-boot normally? 

Hi Lyndon,

Have you checked this device tree file in the kernel code:

https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/arch/arm64/boot/dts/ti/k3-am62-main.dtsi?h=ti-rt-linux-5.10.y where the McASP clocks are being set with assigned parent clocks.

Best Regards

Suren

Hi, yes and it doesn't help. I have tried lots of things in the device tree - see below. I managed to get the refclk assigned to the right parent on the mux and thats all. However, it doesn't seem to set the right frequency or enable the output (Bit 15 of AUDIO_REFCLK0_CTRL_CLKOUT_EN) 

&mcasp0 {
status = "okay";
clock-frequency = <24000000>;
clocks = <&k3_clks 157 0>;
clock-names = "mclk";
assigned-clocks = <&k3_clks 157 0>;
assigned-clock-parents = <&k3_clks 157 7>;

};

BTW. K3conf is out of date in the latest Linux SDK, you need to update it to v0.2 as it is missing the option to set a parent.

Hi Lyndon,

Can you try to enable the TX_DIS (Bit 21) of Pad config register and see if it helps you see the clocks. By default it is disabled.

Ref TRM -> Device Configuration:

Best Regards

Suren

Hi, I suspect that is already being done when from this line:

AM62X_IOPAD(0x01a0, PIN_OUTPUT, 2) /* (E18) MCASP0_AXR0.AUDIO_EXT_REFCLK0 */

I have explained previously how I got the clock to work, by doing this:

// Make MAIN_PLL1_HSDIV6_CLKOUT as a divide by 40 from 960MHz
0x00681098 = 0x00008027
// Enable output and select source as MAIN_PLL1_HSDIV6_CLKOUT)
0x001082E0 = 0x00008006

But there seems to be something missing to do this via the devide tree. Can this please be raised with a CTT expert to suggest what to do?

Is this being investigated? Thank you

Hi Lyndon,

Sorry for the delay in responding. Yes, this is been investigated internally.  Ideally, the assigned-clocks, assigned-clock-parents should have written to the registers by setting the right fields. This is been looked upon. Until then, I would suggest you to manually write to the registers, like the way you have got it working. 

Assuming you want <157 7> clock to be set to 24MHz. Add below line to DT:
assigned-clock-rates = <24000000>;

Let me know if the above line made any difference?

Thanks,

Suren