[PATCH v3 0/3] rtc: rzn1: support XTAL clk and SCMP method

[PATCH v3 0/3] rtc: rzn1: support XTAL clk and SCMP method

[Wolfram Sang]

So far, the code and the binding for the RZ/N1D RTC assumed an input
clock of 32768Hz, so it was not explicitly described. It makes sense to
do this, though. For one reason, clocks with other frequencies might be
used. This RTC supports that via the SCMP counting method. The other
reason is, upcoming SoCs may have only the SCMP method described, so we
need to use it there later.

This series lets the driver handle the optional "xtal" clock and switch
to the SCMP method if suitable. It has been tested on a Renesas RZ/N1D
board with hacked devicetree values.

A branch with updated DTs can be found here:

git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git renesas/n1d/enablement

Looking forward to comments!

Changes since v2:
* don't modify the rtc_ops struct, but have two distinct ones which can
  now be const again (Thanks Miquel, I like it better, too)
* added tag from Miquel (Thanks again)


Wolfram Sang (3):
  dt-bindings: rtc: rzn1: add optional second clock
  rtc: rzn1: Disable controller before initialization
  rtc: rzn1: support input frequencies other than 32768Hz

 .../bindings/rtc/renesas,rzn1-rtc.yaml        |  8 ++-
 drivers/rtc/rtc-rzn1.c                        | 66 +++++++++++++++----
 2 files changed, 61 insertions(+), 13 deletions(-)

-- 
2.47.2

[PATCH v3 1/3] dt-bindings: rtc: rzn1: add optional second clock

[Wolfram Sang]

The external crystal can be a second clock input. It is needed for the
SCMP counting method which allows using crystals different than 32768Hz.
It is also needed for an upcoming SoC which only supports the SCMP
method.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
 .../devicetree/bindings/rtc/renesas,rzn1-rtc.yaml         | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/Documentation/devicetree/bindings/rtc/renesas,rzn1-rtc.yaml b/Documentation/devicetree/bindings/rtc/renesas,rzn1-rtc.yaml
index f6e0c613af67..f6fdcc7090b6 100644
--- a/Documentation/devicetree/bindings/rtc/renesas,rzn1-rtc.yaml
+++ b/Documentation/devicetree/bindings/rtc/renesas,rzn1-rtc.yaml
@@ -33,10 +33,14 @@ properties:
       - const: pps
 
   clocks:
-    maxItems: 1
+    minItems: 1
+    maxItems: 2
 
   clock-names:
-    const: hclk
+    minItems: 1
+    items:
+      - const: hclk
+      - const: xtal
 
   power-domains:
     maxItems: 1
-- 
2.47.2

[PATCH v3 2/3] rtc: rzn1: Disable controller before initialization

[Wolfram Sang]

Datasheet says that the controller must be disabled before setting up
either SUBU or SCMP. This did not matter so far because the driver only
supported SUBU which was the default, too. It is good practice to follow
datasheet recommendations, though. It will also be needed because SCMP
mode will be added in a later patch.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---
 drivers/rtc/rtc-rzn1.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/rtc/rtc-rzn1.c b/drivers/rtc/rtc-rzn1.c
index 3c2861983ff1..7777df1e3426 100644
--- a/drivers/rtc/rtc-rzn1.c
+++ b/drivers/rtc/rtc-rzn1.c
@@ -25,6 +25,7 @@
 #define   RZN1_RTC_CTL0_SLSB_SUBU 0
 #define   RZN1_RTC_CTL0_SLSB_SCMP BIT(4)
 #define   RZN1_RTC_CTL0_AMPM BIT(5)
+#define   RZN1_RTC_CTL0_CEST BIT(6)
 #define   RZN1_RTC_CTL0_CE BIT(7)
 
 #define RZN1_RTC_CTL1 0x04
@@ -369,6 +370,7 @@ static const struct rtc_class_ops rzn1_rtc_ops = {
 static int rzn1_rtc_probe(struct platform_device *pdev)
 {
 	struct rzn1_rtc *rtc;
+	u32 val;
 	int irq;
 	int ret;
 
@@ -406,6 +408,14 @@ static int rzn1_rtc_probe(struct platform_device *pdev)
 	 * Ensure the clock counter is enabled.
 	 * Set 24-hour mode and possible oscillator offset compensation in SUBU mode.
 	 */
+	val = readl(rtc->base + RZN1_RTC_CTL0) & ~RZN1_RTC_CTL0_CE;
+	writel(val, rtc->base + RZN1_RTC_CTL0);
+	/* Wait 2-4 32k clock cycles for the disabled controller */
+	ret = readl_poll_timeout(rtc->base + RZN1_RTC_CTL0, val,
+				 !(val & RZN1_RTC_CTL0_CEST), 62, 123);
+	if (ret)
+		goto dis_runtime_pm;
+
 	writel(RZN1_RTC_CTL0_CE | RZN1_RTC_CTL0_AMPM | RZN1_RTC_CTL0_SLSB_SUBU,
 	       rtc->base + RZN1_RTC_CTL0);
 
-- 
2.47.2

Re: [PATCH v3 2/3] rtc: rzn1: Disable controller before initialization

[Miquel Raynal]

Hello,

On 26/05/2025 at 11:58:03 +02, Wolfram Sang <wsa+renesas@sang-engineering.com> wrote:

> Datasheet says that the controller must be disabled before setting up
> either SUBU or SCMP. This did not matter so far because the driver only
> supported SUBU which was the default, too. It is good practice to follow
> datasheet recommendations, though. It will also be needed because SCMP
> mode will be added in a later patch.
>
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> ---

Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>

Thanks,
Miquèl

[PATCH v3 3/3] rtc: rzn1: support input frequencies other than 32768Hz

[Wolfram Sang]

When using the SCMP mode instead of SUBU, this RTC can also support
other input frequencies than 32768Hz. Also, upcoming SoCs will only
support SCMP.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
---
 drivers/rtc/rtc-rzn1.c | 58 +++++++++++++++++++++++++++++++++---------
 1 file changed, 46 insertions(+), 12 deletions(-)

diff --git a/drivers/rtc/rtc-rzn1.c b/drivers/rtc/rtc-rzn1.c
index 7777df1e3426..c4ed43735457 100644
--- a/drivers/rtc/rtc-rzn1.c
+++ b/drivers/rtc/rtc-rzn1.c
@@ -12,6 +12,7 @@
  */
 
 #include <linux/bcd.h>
+#include <linux/clk.h>
 #include <linux/init.h>
 #include <linux/iopoll.h>
 #include <linux/module.h>
@@ -22,7 +23,6 @@
 #include <linux/spinlock.h>
 
 #define RZN1_RTC_CTL0 0x00
-#define   RZN1_RTC_CTL0_SLSB_SUBU 0
 #define   RZN1_RTC_CTL0_SLSB_SCMP BIT(4)
 #define   RZN1_RTC_CTL0_AMPM BIT(5)
 #define   RZN1_RTC_CTL0_CEST BIT(6)
@@ -50,6 +50,8 @@
 #define   RZN1_RTC_SUBU_DEV BIT(7)
 #define   RZN1_RTC_SUBU_DECR BIT(6)
 
+#define RZN1_RTC_SCMP 0x3c
+
 #define RZN1_RTC_ALM 0x40
 #define RZN1_RTC_ALH 0x44
 #define RZN1_RTC_ALW 0x48
@@ -357,7 +359,7 @@ static int rzn1_rtc_set_offset(struct device *dev, long offset)
 	return 0;
 }
 
-static const struct rtc_class_ops rzn1_rtc_ops = {
+static const struct rtc_class_ops rzn1_rtc_ops_subu = {
 	.read_time = rzn1_rtc_read_time,
 	.set_time = rzn1_rtc_set_time,
 	.read_alarm = rzn1_rtc_read_alarm,
@@ -367,12 +369,21 @@ static const struct rtc_class_ops rzn1_rtc_ops = {
 	.set_offset = rzn1_rtc_set_offset,
 };
 
+static const struct rtc_class_ops rzn1_rtc_ops_scmp = {
+	.read_time = rzn1_rtc_read_time,
+	.set_time = rzn1_rtc_set_time,
+	.read_alarm = rzn1_rtc_read_alarm,
+	.set_alarm = rzn1_rtc_set_alarm,
+	.alarm_irq_enable = rzn1_rtc_alarm_irq_enable,
+};
+
 static int rzn1_rtc_probe(struct platform_device *pdev)
 {
 	struct rzn1_rtc *rtc;
-	u32 val;
-	int irq;
-	int ret;
+	u32 val, scmp_val = 0;
+	struct clk *xtal;
+	unsigned long rate;
+	int irq, ret;
 
 	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
 	if (!rtc)
@@ -395,7 +406,6 @@ static int rzn1_rtc_probe(struct platform_device *pdev)
 	rtc->rtcdev->range_min = RTC_TIMESTAMP_BEGIN_2000;
 	rtc->rtcdev->range_max = RTC_TIMESTAMP_END_2099;
 	rtc->rtcdev->alarm_offset_max = 7 * 86400;
-	rtc->rtcdev->ops = &rzn1_rtc_ops;
 
 	ret = devm_pm_runtime_enable(&pdev->dev);
 	if (ret < 0)
@@ -404,10 +414,24 @@ static int rzn1_rtc_probe(struct platform_device *pdev)
 	if (ret < 0)
 		return ret;
 
-	/*
-	 * Ensure the clock counter is enabled.
-	 * Set 24-hour mode and possible oscillator offset compensation in SUBU mode.
-	 */
+	/* Only switch to scmp if we have an xtal clock with a valid rate and != 32768 */
+	xtal = devm_clk_get_optional(&pdev->dev, "xtal");
+	if (IS_ERR(xtal)) {
+		ret = PTR_ERR(xtal);
+		goto dis_runtime_pm;
+	} else if (xtal) {
+		rate = clk_get_rate(xtal);
+
+		if (rate < 32000 || rate > BIT(22)) {
+			ret = -EOPNOTSUPP;
+			goto dis_runtime_pm;
+		}
+
+		if (rate != 32768)
+			scmp_val = RZN1_RTC_CTL0_SLSB_SCMP;
+	}
+
+	/* Disable controller during SUBU/SCMP setup */
 	val = readl(rtc->base + RZN1_RTC_CTL0) & ~RZN1_RTC_CTL0_CE;
 	writel(val, rtc->base + RZN1_RTC_CTL0);
 	/* Wait 2-4 32k clock cycles for the disabled controller */
@@ -416,8 +440,18 @@ static int rzn1_rtc_probe(struct platform_device *pdev)
 	if (ret)
 		goto dis_runtime_pm;
 
-	writel(RZN1_RTC_CTL0_CE | RZN1_RTC_CTL0_AMPM | RZN1_RTC_CTL0_SLSB_SUBU,
-	       rtc->base + RZN1_RTC_CTL0);
+	/* Set desired modes leaving the controller disabled */
+	writel(RZN1_RTC_CTL0_AMPM | scmp_val, rtc->base + RZN1_RTC_CTL0);
+
+	if (scmp_val) {
+		writel(rate - 1, rtc->base + RZN1_RTC_SCMP);
+		rtc->rtcdev->ops = &rzn1_rtc_ops_scmp;
+	} else {
+		rtc->rtcdev->ops = &rzn1_rtc_ops_subu;
+	}
+
+	/* Enable controller finally */
+	writel(RZN1_RTC_CTL0_CE | RZN1_RTC_CTL0_AMPM | scmp_val, rtc->base + RZN1_RTC_CTL0);
 
 	/* Disable all interrupts */
 	writel(0, rtc->base + RZN1_RTC_CTL1);
-- 
2.47.2

Re: [PATCH v3 0/3] rtc: rzn1: support XTAL clk and SCMP method

[Alexandre Belloni]

On Mon, 26 May 2025 11:58:01 +0200, Wolfram Sang wrote:
> So far, the code and the binding for the RZ/N1D RTC assumed an input
> clock of 32768Hz, so it was not explicitly described. It makes sense to
> do this, though. For one reason, clocks with other frequencies might be
> used. This RTC supports that via the SCMP counting method. The other
> reason is, upcoming SoCs may have only the SCMP method described, so we
> need to use it there later.
> 
> [...]

Applied, thanks!

[1/3] dt-bindings: rtc: rzn1: add optional second clock
      https://git.kernel.org/abelloni/c/ae95a7e32140
[2/3] rtc: rzn1: Disable controller before initialization
      https://git.kernel.org/abelloni/c/a50f00cb87b1
[3/3] rtc: rzn1: support input frequencies other than 32768Hz
      https://git.kernel.org/abelloni/c/f096bdbf08c9

Best regards,

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