2024-04-12 08:03:40

by Wei Fu

Subject: [PATCH 2/5] dt-bindings: rtc: Add optional property "prescaler" in APM X-Gene RTC Document

From: Wei Fu <[email protected]>

Add optional property "prescaler" for APM X-Gene RTC.
The clock source on some platform to RTC is NOT 1HZ,
so we need to prescale the clock to make the input clock become 1HZ,
like (32K/prescaler) = 1HZ on the XuanTie TH1520 AP sub-system RTC.

Signed-off-by: Wei Fu <[email protected]>
---
.../devicetree/bindings/rtc/xgene-rtc.txt | 16 ++++++++++++++++
1 file changed, 16 insertions(+)

diff --git a/Documentation/devicetree/bindings/rtc/xgene-rtc.txt b/Documentation/devicetree/bindings/rtc/xgene-rtc.txt
index fd195c358446..25ba8cf0cc31 100644
--- a/Documentation/devicetree/bindings/rtc/xgene-rtc.txt
+++ b/Documentation/devicetree/bindings/rtc/xgene-rtc.txt
@@ -10,6 +10,9 @@ Required properties:
- #clock-cells: Should be 1.
- clocks: Reference to the clock entry.

+Optional properties:
+- prescaler: Reference to the Value of Counter Prescaler.
+
Example:

rtcclk: rtcclk {
@@ -26,3 +29,16 @@ rtc: rtc@10510000 {
#clock-cells = <1>;
clocks = <&rtcclk 0>;
};
+
+Example XuanTie TH1520 RTC node with Counter Prescaler(prescaler):
+
+rtc: rtc@fffff40000 {
+ compatible = "snps,dw-apb-rtc";
+ reg = <0xff 0xfff40000 0x0 0x1000>;
+ interrupts = <74 IRQ_TYPE_LEVEL_HIGH>;
+ clocks = <&osc_32k>;
+ clock-names = "osc_32k";
+ wakeup-source;
+ prescaler = <0x8000>;
+ status = "okay";
+};
--
2.44.0

2024-04-12 08:32:21

by Alexandre Belloni

Subject: Re: [PATCH 2/5] dt-bindings: rtc: Add optional property "prescaler" in APM X-Gene RTC Document

On 12/04/2024 16:01:44+0800, [email protected] wrote:
> From: Wei Fu <[email protected]>
>
> Add optional property "prescaler" for APM X-Gene RTC.
> The clock source on some platform to RTC is NOT 1HZ,
> so we need to prescale the clock to make the input clock become 1HZ,
> like (32K/prescaler) = 1HZ on the XuanTie TH1520 AP sub-system RTC.
>
> Signed-off-by: Wei Fu <[email protected]>
> ---
> .../devicetree/bindings/rtc/xgene-rtc.txt | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/rtc/xgene-rtc.txt b/Documentation/devicetree/bindings/rtc/xgene-rtc.txt
> index fd195c358446..25ba8cf0cc31 100644
> --- a/Documentation/devicetree/bindings/rtc/xgene-rtc.txt
> +++ b/Documentation/devicetree/bindings/rtc/xgene-rtc.txt
> @@ -10,6 +10,9 @@ Required properties:
> - #clock-cells: Should be 1.
> - clocks: Reference to the clock entry.
>
> +Optional properties:
> +- prescaler: Reference to the Value of Counter Prescaler.

What about getting the input clock rate and calculate the needed
prescaler instead of having it in the device tree?

--
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com