[PATCH 0/2] *** Ricoh RS5C372: add support for Xtal trimming configuration ***

[PATCH 0/2] *** Ricoh RS5C372: add support for Xtal trimming configuration ***

[Pavel Modilaynen]

From: Pavel Modilaynen <pavelmn@axis.com>

*** BLURB HERE ***

Add support for Xtal trimming configuration with new DT property: ricoh,trim.
This uint8 property is to contain raw value to setup Oscillation Adjustment
register (0x7) of Ricoh RS5C372 and similar RTC controllers.
This raw value has device model specific format and is used to adjust
(subtract or add) time counts per second (normally 32768) on regular
intervals (e.g. every 20th second).

Pavel Modilaynen (2):
  rtc: rs5c372: Add support for trim configuration
  dt-bindings: rtc: Add bindings for Ricoh rs5c372

 .../bindings/rtc/ricoh,rs5c372.yaml           | 58 +++++++++++++++++++
 .../devicetree/bindings/rtc/trivial-rtc.yaml  | 12 ----
 drivers/rtc/rtc-rs5c372.c                     | 18 +++++-
 3 files changed, 75 insertions(+), 13 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/rtc/ricoh,rs5c372.yaml

-- 
2.20.1

[PATCH 1/2] rtc: rs5c372: Add support for trim configuration

[Pavel Modilaynen]

From: Pavel Modilaynen <pavelmn@axis.com>

Add support for oscillation adjustment register RS5C372_REG_TRIM
setting that is needed to accommodate for effective crystal
capacitance.

Use optional property ricoh,trim that should contain
raw value to setup this register. According to
datasheets for RS5C372, R2025S/D, RV5C38[67] and R222[13]
the value will be converted to a number of ticks that
is to be subtracted or added when the second digits read
00, 20 or 40 seconds.

Signed-off-by: Pavel Modilaynen <pavelmn@axis.com>
---
 drivers/rtc/rtc-rs5c372.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-rs5c372.c b/drivers/rtc/rtc-rs5c372.c
index 80980414890c..3a2db0326669 100644
--- a/drivers/rtc/rtc-rs5c372.c
+++ b/drivers/rtc/rtc-rs5c372.c
@@ -13,6 +13,7 @@
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/of_device.h>
+#include <linux/of.h>
 
 /*
  * Ricoh has a family of I2C based RTCs, which differ only slightly from
@@ -560,6 +561,8 @@ static int rs5c_oscillator_setup(struct rs5c372 *rs5c372)
 {
 	unsigned char buf[2];
 	int addr, i, ret = 0;
+	struct i2c_client *client = rs5c372->client;
+	u8 trim = 0;
 
 	addr   = RS5C_ADDR(RS5C_REG_CTRL1);
 	buf[0] = rs5c372->regs[RS5C_REG_CTRL1];
@@ -599,9 +602,22 @@ static int rs5c_oscillator_setup(struct rs5c372 *rs5c372)
 		break;
 	}
 
+	/* optional setup of xtal trimming */
+	if (!of_property_read_u8(client->dev.of_node, "ricoh,trim", &trim)) {
+		if (rs5c372->type != rtc_r2221tl && (trim & ~RS5C372_TRIM_MASK)) {
+			dev_warn(&client->dev, "Erroneous setting for ricoh,trim in devicetree\n");
+		} else {
+			int addr = RS5C_ADDR(RS5C372_REG_TRIM);
+			int ret = i2c_smbus_write_byte_data(client, addr, trim);
+
+			if (unlikely(ret < 0))
+				return ret;
+		}
+	}
+
 	for (i = 0; i < sizeof(buf); i++) {
 		addr = RS5C_ADDR(RS5C_REG_CTRL1 + i);
-		ret = i2c_smbus_write_byte_data(rs5c372->client, addr, buf[i]);
+		ret = i2c_smbus_write_byte_data(client, addr, buf[i]);
 		if (unlikely(ret < 0))
 			return ret;
 	}
-- 
2.20.1

[PATCH 2/2] dt-bindings: rtc: Add bindings for Ricoh rs5c372

[Pavel Modilaynen]

From: Pavel Modilaynen <pavelmn@axis.com>

Create new DT bindings yaml file for Ricoh rs5c372 driver
since adding property support naturally deserves it.
Place a description of this property: ricoh,trim.

Signed-off-by: Pavel Modilaynen <pavelmn@axis.com>
---
 .../bindings/rtc/ricoh,rs5c372.yaml           | 58 +++++++++++++++++++
 .../devicetree/bindings/rtc/trivial-rtc.yaml  | 12 ----
 2 files changed, 58 insertions(+), 12 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/rtc/ricoh,rs5c372.yaml

diff --git a/Documentation/devicetree/bindings/rtc/ricoh,rs5c372.yaml b/Documentation/devicetree/bindings/rtc/ricoh,rs5c372.yaml
new file mode 100644
index 000000000000..6cb6a97db5d1
--- /dev/null
+++ b/Documentation/devicetree/bindings/rtc/ricoh,rs5c372.yaml
@@ -0,0 +1,58 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/rtc/ricoh,rs5c372.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Ricoh RS5C372, R2025S/D, RV5C38[67] and R222[13] Real Time Clock
+
+maintainers:
+  - Alexandre Belloni <alexandre.belloni@bootlin.com>
+
+allOf:
+  - $ref: rtc.yaml#
+
+properties:
+  compatible:
+    enum:
+      - ricoh,r2025sd
+      - ricoh,r2221tl
+      - ricoh,rs5c372a
+      - ricoh,rs5c372b
+      - ricoh,rv5c386
+      - ricoh,rv5c387a
+
+  reg:
+    maxItems: 1
+
+  ricoh,trim:
+    $ref: /schemas/types.yaml#/definitions/uint8
+    description: |
+      Raw value of Oscillation Adjustment Register (0x7) which changes
+      time counts of 1 second. Normally, the second counter is incremented
+      once per 32768 clock pulses. The value causes to increment
+      decrement time counts when second digits read 00, 20, 40 seconds
+      (R222[13] can operate on 00 seconds if MSB set).
+      See datasheets for details.
+
+  start-year: true
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        rtc@32 {
+            compatible = "ricoh,r2221tl";
+            reg = <0x32>;
+            ricoh,trim = /bits/ 8 <0x23>;
+        };
+    };
+...
diff --git a/Documentation/devicetree/bindings/rtc/trivial-rtc.yaml b/Documentation/devicetree/bindings/rtc/trivial-rtc.yaml
index 13925bb78ec7..aeabede89654 100644
--- a/Documentation/devicetree/bindings/rtc/trivial-rtc.yaml
+++ b/Documentation/devicetree/bindings/rtc/trivial-rtc.yaml
@@ -55,18 +55,6 @@ properties:
       - nxp,pcf2129
       # Real-time Clock Module
       - pericom,pt7c4338
-      # I2C bus SERIAL INTERFACE REAL-TIME CLOCK IC
-      - ricoh,r2025sd
-      # I2C bus SERIAL INTERFACE REAL-TIME CLOCK IC
-      - ricoh,r2221tl
-      # I2C bus SERIAL INTERFACE REAL-TIME CLOCK IC
-      - ricoh,rs5c372a
-      # I2C bus SERIAL INTERFACE REAL-TIME CLOCK IC
-      - ricoh,rs5c372b
-      # I2C bus SERIAL INTERFACE REAL-TIME CLOCK IC
-      - ricoh,rv5c386
-      # I2C bus SERIAL INTERFACE REAL-TIME CLOCK IC
-      - ricoh,rv5c387a
       # 2-wire CMOS real-time clock
       - sii,s35390a
       # I2C bus SERIAL INTERFACE REAL-TIME CLOCK IC
-- 
2.20.1

Re: [PATCH 1/2] rtc: rs5c372: Add support for trim configuration

[Alexandre Belloni]

Hello,

Please use the proper RTC interface by implementing .set_offset and
.read_offset.

On 31/10/2021 00:50:53+0200, Pavel Modilaynen wrote:
> From: Pavel Modilaynen <pavelmn@axis.com>
> 
> Add support for oscillation adjustment register RS5C372_REG_TRIM
> setting that is needed to accommodate for effective crystal
> capacitance.
> 
> Use optional property ricoh,trim that should contain
> raw value to setup this register. According to
> datasheets for RS5C372, R2025S/D, RV5C38[67] and R222[13]
> the value will be converted to a number of ticks that
> is to be subtracted or added when the second digits read
> 00, 20 or 40 seconds.
> 
> Signed-off-by: Pavel Modilaynen <pavelmn@axis.com>
> ---
>  drivers/rtc/rtc-rs5c372.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/rtc/rtc-rs5c372.c b/drivers/rtc/rtc-rs5c372.c
> index 80980414890c..3a2db0326669 100644
> --- a/drivers/rtc/rtc-rs5c372.c
> +++ b/drivers/rtc/rtc-rs5c372.c
> @@ -13,6 +13,7 @@
>  #include <linux/slab.h>
>  #include <linux/module.h>
>  #include <linux/of_device.h>
> +#include <linux/of.h>
>  
>  /*
>   * Ricoh has a family of I2C based RTCs, which differ only slightly from
> @@ -560,6 +561,8 @@ static int rs5c_oscillator_setup(struct rs5c372 *rs5c372)
>  {
>  	unsigned char buf[2];
>  	int addr, i, ret = 0;
> +	struct i2c_client *client = rs5c372->client;
> +	u8 trim = 0;
>  
>  	addr   = RS5C_ADDR(RS5C_REG_CTRL1);
>  	buf[0] = rs5c372->regs[RS5C_REG_CTRL1];
> @@ -599,9 +602,22 @@ static int rs5c_oscillator_setup(struct rs5c372 *rs5c372)
>  		break;
>  	}
>  
> +	/* optional setup of xtal trimming */
> +	if (!of_property_read_u8(client->dev.of_node, "ricoh,trim", &trim)) {
> +		if (rs5c372->type != rtc_r2221tl && (trim & ~RS5C372_TRIM_MASK)) {
> +			dev_warn(&client->dev, "Erroneous setting for ricoh,trim in devicetree\n");
> +		} else {
> +			int addr = RS5C_ADDR(RS5C372_REG_TRIM);
> +			int ret = i2c_smbus_write_byte_data(client, addr, trim);
> +
> +			if (unlikely(ret < 0))
> +				return ret;
> +		}
> +	}
> +
>  	for (i = 0; i < sizeof(buf); i++) {
>  		addr = RS5C_ADDR(RS5C_REG_CTRL1 + i);
> -		ret = i2c_smbus_write_byte_data(rs5c372->client, addr, buf[i]);
> +		ret = i2c_smbus_write_byte_data(client, addr, buf[i]);
>  		if (unlikely(ret < 0))
>  			return ret;
>  	}
> -- 
> 2.20.1
> 

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

Re: [PATCH 1/2] rtc: rs5c372: Add support for trim configuration

[Pavel Modilaynen]

Hi Alexandre,


On 10/31/21 12:57 AM, Alexandre Belloni wrote:
> Hello,
> 
> Please use the proper RTC interface by implementing .set_offset and
> .read_offset.

I am not sure about .set/read_offset. It looks as runtime adjustment 
interface,
however this Xtal trimming parameter is based on schematics and Xtal 
capacitance (datasheet parameter).
It is found by calibration procedure based on RTC clock output (the 
procedure and calculation of trimming parameter is described in datasheets).
So, I would like to say that this parameter is functionally close to
"quartz-load-femtofarads" for rtc-pcf8523/pcf85063.

> 
> On 31/10/2021 00:50:53+0200, Pavel Modilaynen wrote:
>> From: Pavel Modilaynen <pavelmn@axis.com>
>> 
>> Add support for oscillation adjustment register RS5C372_REG_TRIM
>> setting that is needed to accommodate for effective crystal
>> capacitance.
>> 
>> Use optional property ricoh,trim that should contain
>> raw value to setup this register. According to
>> datasheets for RS5C372, R2025S/D, RV5C38[67] and R222[13]
>> the value will be converted to a number of ticks that
>> is to be subtracted or added when the second digits read
>> 00, 20 or 40 seconds.
>> 
>> Signed-off-by: Pavel Modilaynen <pavelmn@axis.com>
>> ---
>>  drivers/rtc/rtc-rs5c372.c | 18 +++++++++++++++++-
>>  1 file changed, 17 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/rtc/rtc-rs5c372.c b/drivers/rtc/rtc-rs5c372.c
>> index 80980414890c..3a2db0326669 100644
>> --- a/drivers/rtc/rtc-rs5c372.c
>> +++ b/drivers/rtc/rtc-rs5c372.c
>> @@ -13,6 +13,7 @@
>>  #include <linux/slab.h>
>>  #include <linux/module.h>
>>  #include <linux/of_device.h>
>> +#include <linux/of.h>
>>  
>>  /*
>>   * Ricoh has a family of I2C based RTCs, which differ only slightly from
>> @@ -560,6 +561,8 @@ static int rs5c_oscillator_setup(struct rs5c372 *rs5c372)
>>  {
>>        unsigned char buf[2];
>>        int addr, i, ret = 0;
>> +     struct i2c_client *client = rs5c372->client;
>> +     u8 trim = 0;
>>  
>>        addr   = RS5C_ADDR(RS5C_REG_CTRL1);
>>        buf[0] = rs5c372->regs[RS5C_REG_CTRL1];
>> @@ -599,9 +602,22 @@ static int rs5c_oscillator_setup(struct rs5c372 *rs5c372)
>>                break;
>>        }
>>  
>> +     /* optional setup of xtal trimming */
>> +     if (!of_property_read_u8(client->dev.of_node, "ricoh,trim", &trim)) {
>> +             if (rs5c372->type != rtc_r2221tl && (trim & ~RS5C372_TRIM_MASK)) {
>> +                     dev_warn(&client->dev, "Erroneous setting for ricoh,trim in devicetree\n");
>> +             } else {
>> +                     int addr = RS5C_ADDR(RS5C372_REG_TRIM);
>> +                     int ret = i2c_smbus_write_byte_data(client, addr, trim);
>> +
>> +                     if (unlikely(ret < 0))
>> +                             return ret;
>> +             }
>> +     }
>> +
>>        for (i = 0; i < sizeof(buf); i++) {
>>                addr = RS5C_ADDR(RS5C_REG_CTRL1 + i);
>> -             ret = i2c_smbus_write_byte_data(rs5c372->client, addr, buf[i]);
>> +             ret = i2c_smbus_write_byte_data(client, addr, buf[i]);
>>                if (unlikely(ret < 0))
>>                        return ret;
>>        }
>> -- 
>> 2.20.1
>> 
> 
> -- 
> Alexandre Belloni, co-owner and COO, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com <https://bootlin.com>

Re: [PATCH 1/2] rtc: rs5c372: Add support for trim configuration

[Alexandre Belloni]

On 31/10/2021 11:29:12+0100, Pavel Modilaynen wrote:
> On 10/31/21 12:57 AM, Alexandre Belloni wrote:
> > Hello,
> > 
> > Please use the proper RTC interface by implementing .set_offset and
> > .read_offset.
> 
> I am not sure about .set/read_offset. It looks as runtime adjustment
> interface,
> however this Xtal trimming parameter is based on schematics and Xtal
> capacitance (datasheet parameter).
> It is found by calibration procedure based on RTC clock output (the
> procedure and calculation of trimming parameter is described in datasheets).
> So, I would like to say that this parameter is functionally close to
> "quartz-load-femtofarads" for rtc-pcf8523/pcf85063.
> 

quartz-load-femtofarads is for analog trimming which this RTC doesn't
have, both CD and CG are set to 10pF. .set/read_offset are for digital
trimming which is what you are configuring here. You definitively want
to be able to do that at runtime as you need to adjust for temperature
and ageing of the crystal (datasheet, page 14: "For those systems that
have temperature detection precision of clock function may be increased
by correcting clock error according to temperature fluctuations.")

> > 
> > On 31/10/2021 00:50:53+0200, Pavel Modilaynen wrote:
> > > From: Pavel Modilaynen <pavelmn@axis.com>
> > > 
> > > Add support for oscillation adjustment register RS5C372_REG_TRIM
> > > setting that is needed to accommodate for effective crystal
> > > capacitance.
> > > 
> > > Use optional property ricoh,trim that should contain
> > > raw value to setup this register. According to
> > > datasheets for RS5C372, R2025S/D, RV5C38[67] and R222[13]
> > > the value will be converted to a number of ticks that
> > > is to be subtracted or added when the second digits read
> > > 00, 20 or 40 seconds.
> > > 
> > > Signed-off-by: Pavel Modilaynen <pavelmn@axis.com>
> > > ---
> > >   drivers/rtc/rtc-rs5c372.c | 18 +++++++++++++++++-
> > >   1 file changed, 17 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/rtc/rtc-rs5c372.c b/drivers/rtc/rtc-rs5c372.c
> > > index 80980414890c..3a2db0326669 100644
> > > --- a/drivers/rtc/rtc-rs5c372.c
> > > +++ b/drivers/rtc/rtc-rs5c372.c
> > > @@ -13,6 +13,7 @@
> > >   #include <linux/slab.h>
> > >   #include <linux/module.h>
> > >   #include <linux/of_device.h>
> > > +#include <linux/of.h>
> > >   /*
> > >    * Ricoh has a family of I2C based RTCs, which differ only slightly from
> > > @@ -560,6 +561,8 @@ static int rs5c_oscillator_setup(struct rs5c372 *rs5c372)
> > >   {
> > >         unsigned char buf[2];
> > >         int addr, i, ret = 0;
> > > +     struct i2c_client *client = rs5c372->client;
> > > +     u8 trim = 0;
> > >         addr   = RS5C_ADDR(RS5C_REG_CTRL1);
> > >         buf[0] = rs5c372->regs[RS5C_REG_CTRL1];
> > > @@ -599,9 +602,22 @@ static int rs5c_oscillator_setup(struct rs5c372 *rs5c372)
> > >                 break;
> > >         }
> > > +     /* optional setup of xtal trimming */
> > > +     if (!of_property_read_u8(client->dev.of_node, "ricoh,trim", &trim)) {
> > > +             if (rs5c372->type != rtc_r2221tl && (trim & ~RS5C372_TRIM_MASK)) {
> > > +                     dev_warn(&client->dev, "Erroneous setting for ricoh,trim in devicetree\n");
> > > +             } else {
> > > +                     int addr = RS5C_ADDR(RS5C372_REG_TRIM);
> > > +                     int ret = i2c_smbus_write_byte_data(client, addr, trim);
> > > +
> > > +                     if (unlikely(ret < 0))
> > > +                             return ret;
> > > +             }
> > > +     }
> > > +
> > >         for (i = 0; i < sizeof(buf); i++) {
> > >                 addr = RS5C_ADDR(RS5C_REG_CTRL1 + i);
> > > -             ret = i2c_smbus_write_byte_data(rs5c372->client, addr, buf[i]);
> > > +             ret = i2c_smbus_write_byte_data(client, addr, buf[i]);
> > >                 if (unlikely(ret < 0))
> > >                         return ret;
> > >         }
> > > -- 
> > > 2.20.1
> > > 
> > 
> > -- 
> > Alexandre Belloni, co-owner and COO, Bootlin
> > Embedded Linux and Kernel engineering
> > https://bootlin.com <https://bootlin.com>

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

Re: [PATCH 1/2] rtc: rs5c372: Add support for trim configuration

[Pavel Modilaynen]

Hi Alexandre,

On 11/1/21 7:23 PM, Alexandre Belloni wrote:
> On 31/10/2021 11:29:12+0100, Pavel Modilaynen wrote:
>> On 10/31/21 12:57 AM, Alexandre Belloni wrote:
>> > Hello,
>> > 
>> > Please use the proper RTC interface by implementing .set_offset and
>> > .read_offset.
>> 
>> I am not sure about .set/read_offset. It looks as runtime adjustment
>> interface,
>> however this Xtal trimming parameter is based on schematics and Xtal
>> capacitance (datasheet parameter).
>> It is found by calibration procedure based on RTC clock output (the
>> procedure and calculation of trimming parameter is described in datasheets).
>> So, I would like to say that this parameter is functionally close to
>> "quartz-load-femtofarads" for rtc-pcf8523/pcf85063.
>> 
> 
> quartz-load-femtofarads is for analog trimming which this RTC doesn't
> have, both CD and CG are set to 10pF. .set/read_offset are for digital
> trimming which is what you are configuring here. You definitively want
> to be able to do that at runtime as you need to adjust for temperature
> and ageing of the crystal (datasheet, page 14: "For those systems that
> have temperature detection precision of clock function may be increased
> by correcting clock error according to temperature fluctuations.")
>

Thank you for reply.

I am not denying the need in runtime adjustment related to
temperature, aging and precision, which you are referring by excerpt 
from p.14.

I would like to make a point that Xtal trimming is for coarse grained 
adjustment (pages 36-39), primarily related to Xtal capacitance CL (not 
CD/CG). Our goal is to keep a reasonable  drift of ,say, <1 second per 
day and for Xtal that we use with 12.5pF RTC manufacturer recommends 
using 0x23 value for adjustment. In this case we act according to (A) 
course from page 38:

"Adjustment of clock is not made for IC (no adjustment) and any CL value 
may be used for the crystal oscillator. Precision fluctuations of a 
crystal oscillator may be selected as long as clock precision allows. 
Obtain the central frequency as described in section 2.2 using several 
crystal oscillator and ICs, determine an adjustment value as
described in “2.4 Time Trimming Circuit” which shall be set to the 
RS5C372A/B."


>> > 
>> > On 31/10/2021 00:50:53+0200, Pavel Modilaynen wrote:
>> > > From: Pavel Modilaynen <pavelmn@axis.com>
>> > > 
>> > > Add support for oscillation adjustment register RS5C372_REG_TRIM
>> > > setting that is needed to accommodate for effective crystal
>> > > capacitance.
>> > > 
>> > > Use optional property ricoh,trim that should contain
>> > > raw value to setup this register. According to
>> > > datasheets for RS5C372, R2025S/D, RV5C38[67] and R222[13]
>> > > the value will be converted to a number of ticks that
>> > > is to be subtracted or added when the second digits read
>> > > 00, 20 or 40 seconds.
>> > > 
>> > > Signed-off-by: Pavel Modilaynen <pavelmn@axis.com>
>> > > ---
>> > >   drivers/rtc/rtc-rs5c372.c | 18 +++++++++++++++++-
>> > >   1 file changed, 17 insertions(+), 1 deletion(-)
>> > > 
>> > > diff --git a/drivers/rtc/rtc-rs5c372.c b/drivers/rtc/rtc-rs5c372.c
>> > > index 80980414890c..3a2db0326669 100644
>> > > --- a/drivers/rtc/rtc-rs5c372.c
>> > > +++ b/drivers/rtc/rtc-rs5c372.c
>> > > @@ -13,6 +13,7 @@
>> > >   #include <linux/slab.h>
>> > >   #include <linux/module.h>
>> > >   #include <linux/of_device.h>
>> > > +#include <linux/of.h>
>> > >   /*
>> > >    * Ricoh has a family of I2C based RTCs, which differ only slightly from
>> > > @@ -560,6 +561,8 @@ static int rs5c_oscillator_setup(struct rs5c372 *rs5c372)
>> > >   {
>> > >         unsigned char buf[2];
>> > >         int addr, i, ret = 0;
>> > > +     struct i2c_client *client = rs5c372->client;
>> > > +     u8 trim = 0;
>> > >         addr   = RS5C_ADDR(RS5C_REG_CTRL1);
>> > >         buf[0] = rs5c372->regs[RS5C_REG_CTRL1];
>> > > @@ -599,9 +602,22 @@ static int rs5c_oscillator_setup(struct rs5c372 *rs5c372)
>> > >                 break;
>> > >         }
>> > > +     /* optional setup of xtal trimming */
>> > > +     if (!of_property_read_u8(client->dev.of_node, "ricoh,trim", &trim)) {
>> > > +             if (rs5c372->type != rtc_r2221tl && (trim & ~RS5C372_TRIM_MASK)) {
>> > > +                     dev_warn(&client->dev, "Erroneous setting for ricoh,trim in devicetree\n");
>> > > +             } else {
>> > > +                     int addr = RS5C_ADDR(RS5C372_REG_TRIM);
>> > > +                     int ret = i2c_smbus_write_byte_data(client, addr, trim);
>> > > +
>> > > +                     if (unlikely(ret < 0))
>> > > +                             return ret;
>> > > +             }
>> > > +     }
>> > > +
>> > >         for (i = 0; i < sizeof(buf); i++) {
>> > >                 addr = RS5C_ADDR(RS5C_REG_CTRL1 + i);
>> > > -             ret = i2c_smbus_write_byte_data(rs5c372->client, addr, buf[i]);
>> > > +             ret = i2c_smbus_write_byte_data(client, addr, buf[i]);
>> > >                 if (unlikely(ret < 0))
>> > >                         return ret;
>> > >         }
>> > > -- 
>> > > 2.20.1
>> > > 
>> > 
>> > -- 
>> > Alexandre Belloni, co-owner and COO, Bootlin
>> > Embedded Linux and Kernel engineering
>> > https://bootlin.com <https://bootlin.com> <https://bootlin.com 
> <https://bootlin.com>>
> 
> -- 
> Alexandre Belloni, co-owner and COO, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com <https://bootlin.com>

Re: [PATCH 1/2] rtc: rs5c372: Add support for trim configuration

[Alexandre Belloni]

On 02/11/2021 00:14:39+0100, Pavel Modilaynen wrote:
> Hi Alexandre,
> 
> On 11/1/21 7:23 PM, Alexandre Belloni wrote:
> > On 31/10/2021 11:29:12+0100, Pavel Modilaynen wrote:
> > > On 10/31/21 12:57 AM, Alexandre Belloni wrote:
> > > > Hello,
> > > > > Please use the proper RTC interface by implementing .set_offset
> > > and
> > > > .read_offset.
> > > 
> > > I am not sure about .set/read_offset. It looks as runtime adjustment
> > > interface,
> > > however this Xtal trimming parameter is based on schematics and Xtal
> > > capacitance (datasheet parameter).
> > > It is found by calibration procedure based on RTC clock output (the
> > > procedure and calculation of trimming parameter is described in datasheets).
> > > So, I would like to say that this parameter is functionally close to
> > > "quartz-load-femtofarads" for rtc-pcf8523/pcf85063.
> > > 
> > 
> > quartz-load-femtofarads is for analog trimming which this RTC doesn't
> > have, both CD and CG are set to 10pF. .set/read_offset are for digital
> > trimming which is what you are configuring here. You definitively want
> > to be able to do that at runtime as you need to adjust for temperature
> > and ageing of the crystal (datasheet, page 14: "For those systems that
> > have temperature detection precision of clock function may be increased
> > by correcting clock error according to temperature fluctuations.")
> > 
> 
> Thank you for reply.
> 
> I am not denying the need in runtime adjustment related to
> temperature, aging and precision, which you are referring by excerpt from
> p.14.
> 
> I would like to make a point that Xtal trimming is for coarse grained
> adjustment (pages 36-39), primarily related to Xtal capacitance CL (not
> CD/CG). Our goal is to keep a reasonable  drift of ,say, <1 second per day
> and for Xtal that we use with 12.5pF RTC manufacturer recommends using 0x23
> value for adjustment. In this case we act according to (A) course from page
> 38:
> 
> "Adjustment of clock is not made for IC (no adjustment) and any CL value may
> be used for the crystal oscillator. Precision fluctuations of a crystal
> oscillator may be selected as long as clock precision allows. Obtain the
> central frequency as described in section 2.2 using several crystal
> oscillator and ICs, determine an adjustment value as
> described in “2.4 Time Trimming Circuit” which shall be set to the
> RS5C372A/B."
> 

This doesn't prevent you from using the .set/read_offset interface.
Simply have a startup script that forcibly set the hardcoded value if
this is what you want. However, I'm pretty sure your products have NTP
which allows to precisely set a calculated value instead of an hardcoded
one.

> 
> > > > > On 31/10/2021 00:50:53+0200, Pavel Modilaynen wrote:
> > > > > From: Pavel Modilaynen <pavelmn@axis.com>
> > > > > > > Add support for oscillation adjustment register
> > > RS5C372_REG_TRIM
> > > > > setting that is needed to accommodate for effective crystal
> > > > > capacitance.
> > > > > > > Use optional property ricoh,trim that should contain
> > > > > raw value to setup this register. According to
> > > > > datasheets for RS5C372, R2025S/D, RV5C38[67] and R222[13]
> > > > > the value will be converted to a number of ticks that
> > > > > is to be subtracted or added when the second digits read
> > > > > 00, 20 or 40 seconds.
> > > > > > > Signed-off-by: Pavel Modilaynen <pavelmn@axis.com>
> > > > > ---
> > > > >   drivers/rtc/rtc-rs5c372.c | 18 +++++++++++++++++-
> > > > >   1 file changed, 17 insertions(+), 1 deletion(-)
> > > > > > > diff --git a/drivers/rtc/rtc-rs5c372.c
> > > b/drivers/rtc/rtc-rs5c372.c
> > > > > index 80980414890c..3a2db0326669 100644
> > > > > --- a/drivers/rtc/rtc-rs5c372.c
> > > > > +++ b/drivers/rtc/rtc-rs5c372.c
> > > > > @@ -13,6 +13,7 @@
> > > > >   #include <linux/slab.h>
> > > > >   #include <linux/module.h>
> > > > >   #include <linux/of_device.h>
> > > > > +#include <linux/of.h>
> > > > >   /*
> > > > >    * Ricoh has a family of I2C based RTCs, which differ only slightly from
> > > > > @@ -560,6 +561,8 @@ static int rs5c_oscillator_setup(struct rs5c372 *rs5c372)
> > > > >   {
> > > > >         unsigned char buf[2];
> > > > >         int addr, i, ret = 0;
> > > > > +     struct i2c_client *client = rs5c372->client;
> > > > > +     u8 trim = 0;
> > > > >         addr   = RS5C_ADDR(RS5C_REG_CTRL1);
> > > > >         buf[0] = rs5c372->regs[RS5C_REG_CTRL1];
> > > > > @@ -599,9 +602,22 @@ static int rs5c_oscillator_setup(struct rs5c372 *rs5c372)
> > > > >                 break;
> > > > >         }
> > > > > +     /* optional setup of xtal trimming */
> > > > > +     if (!of_property_read_u8(client->dev.of_node, "ricoh,trim", &trim)) {
> > > > > +             if (rs5c372->type != rtc_r2221tl && (trim & ~RS5C372_TRIM_MASK)) {
> > > > > +                     dev_warn(&client->dev, "Erroneous setting for ricoh,trim in devicetree\n");
> > > > > +             } else {
> > > > > +                     int addr = RS5C_ADDR(RS5C372_REG_TRIM);
> > > > > +                     int ret = i2c_smbus_write_byte_data(client, addr, trim);
> > > > > +
> > > > > +                     if (unlikely(ret < 0))
> > > > > +                             return ret;
> > > > > +             }
> > > > > +     }
> > > > > +
> > > > >         for (i = 0; i < sizeof(buf); i++) {
> > > > >                 addr = RS5C_ADDR(RS5C_REG_CTRL1 + i);
> > > > > -             ret = i2c_smbus_write_byte_data(rs5c372->client, addr, buf[i]);
> > > > > +             ret = i2c_smbus_write_byte_data(client, addr, buf[i]);
> > > > >                 if (unlikely(ret < 0))
> > > > >                         return ret;
> > > > >         }
> > > > > -- > > 2.20.1
> > > > > > > -- > Alexandre Belloni, co-owner and COO, Bootlin
> > > > Embedded Linux and Kernel engineering
> > > > https://bootlin.com <https://bootlin.com> <https://bootlin.com
> > <https://bootlin.com>>
> > 
> > -- 
> > Alexandre Belloni, co-owner and COO, Bootlin
> > Embedded Linux and Kernel engineering
> > https://bootlin.com <https://bootlin.com>

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