The m41t82 and m41t83 have an adjustable internal capacitance that
defaults to 25 pF per xtal pin. This patch series adds the ability to
configure it via the devicetree.
Patch 1 just switches the CONFIG_OF-dependent block in m41t80_probe()
from an ifdef guard to an if(IS_ENABLED(...)) guard, so that I don't
need to use __maybe_used on my new functions and variables.
Patch 2 is the DeviceTree YAML changes.
Patch 3 is the actual added functionality.
The desired capacitance comes from quartz-load-capacitance property,
following the example of two other RTC ICs that have adjustable internal
load capacitance, the NXP pcf85063 and pcf8523.
The m41t82 supports much finer-grained control over the capacitance than
those chips and calls the feature "analog calibration", but it looks to
me like it's essentially the same kind of thing.
My use case for this is:
ST specifies not to add any additional external load capacitance[1], but
the MikroElektronika RTC 9 Click board[2] has a 22 pF cap on each xtal
pin[3]. The resulting combined capacitance appears to be outside of the
operating range of the xtal, because when power is removed from the
boards I'm testing with, the RTC reports an Oscillator-Fail flag on the
next power on.
I found I could work around the problem by reducing the internal load
capacitance as low as it will go.
I have tested on the VersaLogic Zebra, an NXP i.MX6 ARM. I made sure it
compiles cleanly on amd64 with CONFIG_OF=no.
References:
[1] https://www.st.com/resource/en/application_note/an3060-applications-guide-for-serial-realtime-clocks-rtcs-stmicroelectronics.pdf
[2] https://www.mikroe.com/rtc-9-click
[3] https://download.mikroe.com/documents/add-on-boards/click/rtc-9/rtc-9-click-schematic-v100.pdf
Dennis Lambe Jr (3):
rtc: m41t80: probe: use IS_ENABLED for CONFIG_OF
dt-bindings: m41t80: add xtal load capacitance
rtc: m41t80: set xtal load capacitance from DT
.../devicetree/bindings/rtc/st,m41t80.yaml | 18 ++++
drivers/rtc/rtc-m41t80.c | 84 +++++++++++++++++--
2 files changed, 94 insertions(+), 8 deletions(-)
--
2.25.1
The style guide recommends IS_ENABLED rather than ifdef for wrapping
conditional code wherever possible.
Functions that are only called on DeviceTree platforms would otherwise
need to be cluttered up with __maybe_unused, which is especially
undesireable if there's nothing inherently DT-specific about those
functions.
Signed-off-by: Dennis Lambe Jr <[email protected]>
---
drivers/rtc/rtc-m41t80.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/drivers/rtc/rtc-m41t80.c b/drivers/rtc/rtc-m41t80.c
index 494052dbd39f..f963b76e5fc0 100644
--- a/drivers/rtc/rtc-m41t80.c
+++ b/drivers/rtc/rtc-m41t80.c
@@ -909,10 +909,11 @@ static int m41t80_probe(struct i2c_client *client)
if (IS_ERR(m41t80_data->rtc))
return PTR_ERR(m41t80_data->rtc);
-#ifdef CONFIG_OF
- wakeup_source = of_property_read_bool(client->dev.of_node,
- "wakeup-source");
-#endif
+ if (IS_ENABLED(CONFIG_OF)) {
+ wakeup_source = of_property_read_bool(client->dev.of_node,
+ "wakeup-source");
+ }
+
if (client->irq > 0) {
rc = devm_request_threaded_irq(&client->dev, client->irq,
NULL, m41t80_handle_irq,
--
2.25.1
Add support for specifying the xtal load capacitance in the DT node for
devices with an Analog Calibration register.
the m41t82 and m41t83 support xtal load capacitance from 3.5 pF to 17.4
pF.
If no xtal load capacitance is specified, the battery-backed register
won't be modified. The hardware defaults to 12.5 pF on reset.
Signed-off-by: Dennis Lambe Jr <[email protected]>
---
drivers/rtc/rtc-m41t80.c | 75 +++++++++++++++++++++++++++++++++++++---
1 file changed, 71 insertions(+), 4 deletions(-)
diff --git a/drivers/rtc/rtc-m41t80.c b/drivers/rtc/rtc-m41t80.c
index f963b76e5fc0..85bde7130a4d 100644
--- a/drivers/rtc/rtc-m41t80.c
+++ b/drivers/rtc/rtc-m41t80.c
@@ -44,12 +44,17 @@
#define M41T80_REG_ALARM_MIN 0x0d
#define M41T80_REG_ALARM_SEC 0x0e
#define M41T80_REG_FLAGS 0x0f
+#define M41T80_REG_AC 0x12
#define M41T80_REG_SQW 0x13
#define M41T80_DATETIME_REG_SIZE (M41T80_REG_YEAR + 1)
#define M41T80_ALARM_REG_SIZE \
(M41T80_REG_ALARM_SEC + 1 - M41T80_REG_ALARM_MON)
+#define M41T80_AC_MIN 3500
+#define M41T80_AC_MAX 17375
+#define M41T80_AC_DEFAULT 12500
+
#define M41T80_SQW_MAX_FREQ 32768
#define M41T80_SEC_ST BIT(7) /* ST: Stop Bit */
@@ -68,6 +73,7 @@
#define M41T80_FEATURE_SQ BIT(2) /* Squarewave feature */
#define M41T80_FEATURE_WD BIT(3) /* Extra watchdog resolution */
#define M41T80_FEATURE_SQ_ALT BIT(4) /* RSx bits are in reg 4 */
+#define M41T80_FEATURE_AC BIT(5) /* Analog calibration */
static const struct i2c_device_id m41t80_id[] = {
{ "m41t62", M41T80_FEATURE_SQ | M41T80_FEATURE_SQ_ALT },
@@ -75,8 +81,10 @@ static const struct i2c_device_id m41t80_id[] = {
{ "m41t80", M41T80_FEATURE_SQ },
{ "m41t81", M41T80_FEATURE_HT | M41T80_FEATURE_SQ},
{ "m41t81s", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ },
- { "m41t82", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ },
- { "m41t83", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ },
+ { "m41t82", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ
+ | M41T80_FEATURE_AC },
+ { "m41t83", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ
+ | M41T80_FEATURE_AC },
{ "m41st84", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ },
{ "m41st85", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ },
{ "m41st87", M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ },
@@ -108,11 +116,13 @@ static const __maybe_unused struct of_device_id m41t80_of_match[] = {
},
{
.compatible = "st,m41t82",
- .data = (void *)(M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ)
+ .data = (void *)(M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ
+ | M41T80_FEATURE_AC)
},
{
.compatible = "st,m41t83",
- .data = (void *)(M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ)
+ .data = (void *)(M41T80_FEATURE_HT | M41T80_FEATURE_BL | M41T80_FEATURE_SQ
+ | M41T80_FEATURE_AC)
},
{
.compatible = "st,m41t84",
@@ -405,6 +415,54 @@ static const struct rtc_class_ops m41t80_rtc_ops = {
.alarm_irq_enable = m41t80_alarm_irq_enable,
};
+static u8 to_sign_magnitude_u8(int n)
+{
+ if (n < 0)
+ return 0x80 | -n;
+ return n;
+}
+
+static int m41t80_encode_ac(int quartz_load)
+{
+ if (quartz_load < M41T80_AC_MIN || quartz_load > M41T80_AC_MAX)
+ return -EINVAL;
+
+ /*
+ * register representation is the per-capacitor offset from its default
+ * value in units of 1/4 pF, in sign-magnitude form.
+ */
+ return to_sign_magnitude_u8((quartz_load - M41T80_AC_DEFAULT) / 125);
+}
+
+static int m41t80_set_ac(struct m41t80_data *m41t80_data, int quartz_load)
+{
+ struct i2c_client *client = m41t80_data->client;
+ struct device *dev = &client->dev;
+ int ret;
+ int ac;
+
+ if (!(m41t80_data->features & M41T80_FEATURE_AC)) {
+ dev_err(dev, "analog calibration requested but not supported\n");
+ return -EOPNOTSUPP;
+ }
+
+ ac = m41t80_encode_ac(quartz_load);
+ if (ac < 0) {
+ dev_err(dev, "quartz load %d fF out of range\n",
+ quartz_load);
+ return ac;
+ }
+
+ ret = i2c_smbus_write_byte_data(client, M41T80_REG_AC, ac);
+ if (ret < 0) {
+ dev_err(dev, "Can't set AC register\n");
+ return ret;
+ }
+
+ dev_info(dev, "quartz load set to %d fF (AC=0x%x)\n", quartz_load, ac);
+ return 0;
+}
+
#ifdef CONFIG_PM_SLEEP
static int m41t80_suspend(struct device *dev)
{
@@ -883,6 +941,7 @@ static int m41t80_probe(struct i2c_client *client)
struct rtc_time tm;
struct m41t80_data *m41t80_data = NULL;
bool wakeup_source = false;
+ u32 quartz_load = M41T80_AC_DEFAULT;
if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_I2C_BLOCK |
I2C_FUNC_SMBUS_BYTE_DATA)) {
@@ -912,6 +971,14 @@ static int m41t80_probe(struct i2c_client *client)
if (IS_ENABLED(CONFIG_OF)) {
wakeup_source = of_property_read_bool(client->dev.of_node,
"wakeup-source");
+
+ rc = of_property_read_u32(client->dev.of_node,
+ "quartz-load-femtofarads",
+ &quartz_load);
+ if (!rc)
+ m41t80_set_ac(m41t80_data, quartz_load);
+ else if (rc != -EINVAL)
+ dev_err(&client->dev, "quartz-load-femtofarads property value is missing or invalid\n");
}
if (client->irq > 0) {
--
2.25.1
The ST m41t82 and m41t83 support programmable load capacitance from 3.5
pF to 17.4 pF. The hardware defaults to 12.5 pF.
The accuracy of the xtal can be calibrated precisely by adjusting the
load capacicance.
Add default, minimum, and maximum for the standard rtc property
quartz-load-femtofarads on compatible devices.
Signed-off-by: Dennis Lambe Jr <[email protected]>
---
.../devicetree/bindings/rtc/st,m41t80.yaml | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/Documentation/devicetree/bindings/rtc/st,m41t80.yaml b/Documentation/devicetree/bindings/rtc/st,m41t80.yaml
index fc9c6da6483f..6b72580dc031 100644
--- a/Documentation/devicetree/bindings/rtc/st,m41t80.yaml
+++ b/Documentation/devicetree/bindings/rtc/st,m41t80.yaml
@@ -33,6 +33,11 @@ properties:
"#clock-cells":
const: 1
+ quartz-load-femtofarads:
+ default: 12500
+ minimum: 3500
+ maximum: 17375
+
clock-output-names:
maxItems: 1
description: From common clock binding to override the default output clock name.
@@ -44,8 +49,21 @@ properties:
clock-frequency:
const: 32768
+ wakeup-source: true
+
allOf:
- $ref: rtc.yaml
+ - if:
+ not:
+ properties:
+ compatible:
+ contains:
+ enum:
+ - st,m41t82
+ - st,m41t83
+ then:
+ properties:
+ quartz-load-femtofarads: false
unevaluatedProperties: false
--
2.25.1
On 19/12/2022 20:09, Dennis Lambe Jr wrote:
> The ST m41t82 and m41t83 support programmable load capacitance from 3.5
> pF to 17.4 pF. The hardware defaults to 12.5 pF.
>
> The accuracy of the xtal can be calibrated precisely by adjusting the
> load capacicance.
>
> Add default, minimum, and maximum for the standard rtc property
> quartz-load-femtofarads on compatible devices.
>
> Signed-off-by: Dennis Lambe Jr <[email protected]>
> ---
> .../devicetree/bindings/rtc/st,m41t80.yaml | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/rtc/st,m41t80.yaml b/Documentation/devicetree/bindings/rtc/st,m41t80.yaml
> index fc9c6da6483f..6b72580dc031 100644
> --- a/Documentation/devicetree/bindings/rtc/st,m41t80.yaml
> +++ b/Documentation/devicetree/bindings/rtc/st,m41t80.yaml
> @@ -33,6 +33,11 @@ properties:
> "#clock-cells":
> const: 1
>
> + quartz-load-femtofarads:
> + default: 12500
> + minimum: 3500
> + maximum: 17375
> +
> clock-output-names:
> maxItems: 1
> description: From common clock binding to override the default output clock name.
> @@ -44,8 +49,21 @@ properties:
> clock-frequency:
> const: 32768
>
> + wakeup-source: true
Why do you need it here? It's already accepted in rtc.yaml. Adding it is
not explained in commit msg.
> +
> allOf:
Best regards,
Krzysztof
On Tue, Dec 20, 2022 at 5:52 AM Krzysztof Kozlowski
<[email protected]> wrote:
> > + wakeup-source: true
>
> Why do you need it here? It's already accepted in rtc.yaml. Adding it is
> not explained in commit msg.
This shouldn't have been included in the patch, my mistake. In the
next revision of the patch series I'll take this line out. Sorry about
that, thanks for catching it.
Aside from that, does this patch look good to you? It passed
dt_binding_check and reflects my understanding of the logic needed,
but dt-binding yaml isn't something I'm super familiar with,
especially the if: not: properties: contains: enum block. The
intention is to indicate that the `quartz-load-femtofarads` property
is only applicable to the m41t82 and m41t83, but not the other devices
supported by the rtc-m41t80 driver.
--
Dennis Lambe (He/Him)
Lead Firmware Engineer
sparkcharge.io