On Tue, 29 Oct 2024 at 15:31, Jie Luo [off-list ref] wrote:

On 10/28/2024 11:39 PM, Dmitry Baryshkov wrote:

quoted

On Mon, Oct 28, 2024 at 10:04:11PM +0800, Luo Jie wrote:

quoted

The CMN PLL clock controller allows selection of an input clock rate
from a defined set of input clock rates. It in-turn supplies fixed
rate output clocks to the hardware blocks that provide the ethernet
functions such as PPE (Packet Process Engine) and connected switch or
PHY, and to GCC.

The reference clock of CMN PLL is routed from XO to the CMN PLL through
the internal WiFi block.
.XO (48 MHZ or 96 MHZ)-->WiFi (multiplier/divider)-->48 MHZ to CMN PLL.

The reference input clock from WiFi to CMN PLL is fully controlled by
the bootstrap pins which select the XO frequency (48 MHZ or 96 MHZ).
Based on this frequency, the divider in the internal Wi-Fi block is
automatically configured by hardware (1 for 48 MHZ, 2 for 96 MHZ), to
ensure output clock to CMN PLL is 48 MHZ.

Signed-off-by: Luo Jie <redacted>
---
  arch/arm64/boot/dts/qcom/ipq9574-rdp-common.dtsi | 16 ++++++++++++++-
  arch/arm64/boot/dts/qcom/ipq9574.dtsi            | 26 +++++++++++++++++++++++-
  2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/boot/dts/qcom/ipq9574-rdp-common.dtsi b/arch/arm64/boot/dts/qcom/ipq9574-rdp-common.dtsi
index 91e104b0f865..f026c2a9d0c0 100644
--- a/arch/arm64/boot/dts/qcom/ipq9574-rdp-common.dtsi
+++ b/arch/arm64/boot/dts/qcom/ipq9574-rdp-common.dtsi

@@ -3,7 +3,7 @@
   * IPQ9574 RDP board common device tree source
   *
   * Copyright (c) 2020-2021 The Linux Foundation. All rights reserved.
- * Copyright (c) 2023, Qualcomm Innovation Center, Inc. All rights reserved.
+ * Copyright (c) 2023-2024, Qualcomm Innovation Center, Inc. All rights reserved.
   */

  /dts-v1/;

@@ -164,6 +164,20 @@ &usb3 {
     status = "okay";
  };

+/*
+ * The bootstrap pins for the board select the XO clock frequency,
+ * which automatically enables the right dividers to ensure the
+ * reference clock output to CMNPLL is 48 MHZ.
+ */
+&cmn_pll_ref_clk {
+    clock-div = <1>;
+    clock-mult = <1>;
+};
+
  &xo_board_clk {
     clock-frequency = <24000000>;
  };
+
+&xo_clk {
+    clock-frequency = <48000000>;
+};

diff --git a/arch/arm64/boot/dts/qcom/ipq9574.dtsi b/arch/arm64/boot/dts/qcom/ipq9574.dtsi
index 14c7b3a78442..ad9cdb1f76db 100644
--- a/arch/arm64/boot/dts/qcom/ipq9574.dtsi
+++ b/arch/arm64/boot/dts/qcom/ipq9574.dtsi

@@ -3,10 +3,11 @@
   * IPQ9574 SoC device tree source
   *
   * Copyright (c) 2020-2021 The Linux Foundation. All rights reserved.
- * Copyright (c) 2023, Qualcomm Innovation Center, Inc. All rights reserved.
+ * Copyright (c) 2023-2024, Qualcomm Innovation Center, Inc. All rights reserved.
   */

  #include <dt-bindings/clock/qcom,apss-ipq.h>
+#include <dt-bindings/clock/qcom,ipq-cmn-pll.h>
  #include <dt-bindings/clock/qcom,ipq9574-gcc.h>
  #include <dt-bindings/interconnect/qcom,ipq9574.h>
  #include <dt-bindings/interrupt-controller/arm-gic.h>

@@ -19,6 +20,12 @@ / {
     #size-cells = <2>;

     clocks {
+            cmn_pll_ref_clk: cmn-pll-ref-clk {
+                    compatible = "fixed-factor-clock";
+                    clocks = <&xo_clk>;
+                    #clock-cells = <0>;
+            };
+
             sleep_clk: sleep-clk {
                     compatible = "fixed-clock";
                     #clock-cells = <0>;

@@ -28,6 +35,11 @@ xo_board_clk: xo-board-clk {
                     compatible = "fixed-clock";
                     #clock-cells = <0>;
             };
+
+            xo_clk: xo-clk {
+                    compatible = "fixed-clock";
+                    #clock-cells = <0>;
+            };

What is the difference between xo_clk and xo_board_clk? Are there two
different crystals?

The xo_board_clk of 24 MHZ is generated by applying another divider in
HW (by 2), on top of the same 48 MHZ clock output from internal Wi-Fi.

XO (48 MHZ or 96 MHZ)-->WiFi (mul/div)-->48 MHZ-->fixed factor divider 2
by HW ---> xo_board_clk (24 MHZ)

We may need to correct its clock chain representation. We will update
xo_board_clk as a fixed factor (div by 2) clock, and refer to the 48 MHZ
input clock, using a separate patch after the CMN PLL patch series
review is concluded. Hope this approach is fine.

Yes, please. Don't try to 'shortcut' the hardware description.
Describing the actual hardware is the best way to work.

-- 
With best wishes
Dmitry