linux-kernel - [PATCH v2 2/3] rtc: pcf8523: Make DSM for battery switch-over configurable from DT

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Date:   Mon, 20 Jul 2020 12:24:00 +0100
From:   miguelborgesdefreitas@...il.com
To:     a.zummo@...ertech.it
Cc:     baruch@...s.co.il, linux@...linux.org.uk,
        alexandre.belloni@...tlin.com, robh+dt@...nel.org,
        shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
        festevam@...il.com, linux-imx@....com,
        miguelborgesdefreitas@...il.com, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/3] rtc: pcf8523: Make DSM for battery switch-over configurable from DT

From: Miguel Borges de Freitas <miguelborgesdefreitas@...il.com>

The pcf8523 has two configurable modes for the battery switch-over
functionality: (i) the default mode and (ii) the direct switching mode -
the driver atm only supports (i). For the default mode to work a filtering
circuit consisting of a series resistor of 1 kOhm and a capacitor of 3.3
microF must be added to the VDD pin input to guarantee a voltage drop of
less 0.7V/ms for the oscillator operation reliability (see pp.54 of the
datasheet). Some boards (e.g. the cubox-i) do not include such circuitry
and are designed to work only in direct switching mode. According to the
datasheet, this is the recommended mode for hw designs where VDD is always
expected to be higher than VBAT. After a power cycle, if the voltage drop
exceeds the said value, the REG_SECONDS_OS bit will be set (oscillator has
stopped or been interrupted) causing userspace applications such as
timedatectl and hwclock to fail (RTC_RD_TIME: Invalid argument).
Hence, This enables DSM as a device-tree configurable property so that
specific boards can make use of it. Note that, if the RTC comes from an
inconsistent state (REG_SECONDS_OS defined), the software reset will
override any power management options set during the probe phase.
Thus, pm is also enforced in pcf8523_start_rtc.

Signed-off-by: Miguel Borges de Freitas <miguelborgesdefreitas@...il.com>
---
Changes in v2:
- Added extended commit message for git history
- Separate dt bindings documentation into a single patch

 drivers/rtc/rtc-pcf8523.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/rtc/rtc-pcf8523.c b/drivers/rtc/rtc-pcf8523.c
index 47e0f41..0c08f91 100644
--- a/drivers/rtc/rtc-pcf8523.c
+++ b/drivers/rtc/rtc-pcf8523.c
@@ -122,7 +122,7 @@ static int pcf8523_load_capacitance(struct i2c_client *client)
 	return err;
 }

-static int pcf8523_set_pm(struct i2c_client *client, u8 pm)
+static int pcf8523_set_pm(struct i2c_client *client)
 {
 	u8 value;
 	int err;
@@ -131,7 +131,10 @@ static int pcf8523_set_pm(struct i2c_client *client, u8 pm)
 	if (err < 0)
 		return err;

-	value = (value & ~REG_CONTROL3_PM_MASK) | pm;
+	if (of_property_read_bool(client->dev.of_node, "pm-enable-dsm"))
+		value = (value & ~REG_CONTROL3_PM_MASK) | REG_CONTROL3_PM_DSM;
+	else
+		value = (value & ~REG_CONTROL3_PM_MASK) | 0;

 	err = pcf8523_write(client, REG_CONTROL3, value);
 	if (err < 0)
@@ -173,6 +176,10 @@ static int pcf8523_start_rtc(struct i2c_client *client)
 	if (err < 0)
 		return err;

+	err = pcf8523_set_pm(client);
+	if (err < 0)
+		return err;
+
 	return 0;
 }

@@ -352,7 +359,7 @@ static int pcf8523_probe(struct i2c_client *client,
 		dev_warn(&client->dev, "failed to set xtal load capacitance: %d",
 			 err);

-	err = pcf8523_set_pm(client, 0);
+	err = pcf8523_set_pm(client);
 	if (err < 0)
 		return err;

-- 
1.8.3.1