[PATCH v4 0/2] sy7636a: power the panel only during updates

[PATCH v4 0/2] sy7636a: power the panel only during updates

[Pablo Mazzini]

The SY7636A hwmon driver keeps VCOM on from probe, so a display driver
can not power the panel only during updates.

Read the temperature only while the rails are on instead.

This is based on regulator for-7.5, which has the rest of the series.
Patch 1 depends on "regulator: sy7636a: bind to the I2C device directly"
there.

Tested on a PocketBook Verse (B288).

v4:
- drop the patches applied by Mark and Guenter
- patch 1: keep the hwmon name (Guenter)

v3:
- drop the applied patches 1-3
- new patch: no wait when power good is already high (Mark)
- move the I2C binding before the hwmon read change, so the hwmon driver
  only probes once vin is on (Andreas)
- explain in a comment why power good gates the read, and its
  limitation (Guenter, Andreas)

v2:
- drop the DT patch keeping VCOM always-on (Andreas)
- only wait for power good, VCOM_EN stays as it was (Andreas)
- new patch: fix negative temperatures
- keep the temperature in drivers/hwmon as an auxiliary driver of the
  regulator, instead of moving it into the regulator driver (Guenter,
  Andreas)
- no VCOM enable at probe, which also removes the probe race
- read power good and the temperature in one transfer (Andreas)

Pablo Mazzini (2):
  hwmon: sy7636a: read the temperature only while the rails are on
  ARM: imx_v6_v7_defconfig: drop the SY7636A MFD option

 arch/arm/configs/imx_v6_v7_defconfig |  1 -
 drivers/hwmon/sy7636a-hwmon.c        | 35 +++++++++++++++++++---------
 2 files changed, 24 insertions(+), 12 deletions(-)


base-commit: 89b552ff49551960b9e270feee888a0298a12d94
-- 
2.52.0

[PATCH v4 1/2] hwmon: sy7636a: read the temperature only while the rails are on

[Pablo Mazzini]

The driver enables VCOM at probe, which keeps the panel's high voltage
rails on for good. Read the temperature only while the rails are on, when
the chip samples it, and return -ENODATA otherwise. Read power good with
it in one transfer, so the value can not be from before the first sample
or after the rails went off.

Signed-off-by: Pablo Mazzini <pmazzini@gmail.com>
---
 drivers/hwmon/sy7636a-hwmon.c | 35 ++++++++++++++++++++++++-----------
 1 file changed, 24 insertions(+), 11 deletions(-)

diff --git a/drivers/hwmon/sy7636a-hwmon.c b/drivers/hwmon/sy7636a-hwmon.c
index a0d0b4119bb3..a8bfbf1716a1 100644
--- a/drivers/hwmon/sy7636a-hwmon.c
+++ b/drivers/hwmon/sy7636a-hwmon.c
@@ -9,26 +9,43 @@
  */
 
 #include <linux/auxiliary_bus.h>
+#include <linux/bits.h>
 #include <linux/err.h>
 #include <linux/hwmon.h>
 #include <linux/module.h>
 #include <linux/regmap.h>
-#include <linux/regulator/machine.h>
 
-#define SY7636A_REG_TERMISTOR_READOUT	0x08
+#define SY7636A_REG_FAULT_FLAG		0x07
+#define SY7636A_FAULT_FLAG_PG		BIT(0)
 
 static int sy7636a_read(struct device *dev, enum hwmon_sensor_types type,
 			u32 attr, int channel, long *temp)
 {
 	struct regmap *regmap = dev_get_drvdata(dev);
-	int ret, reg_val;
-
-	ret = regmap_read(regmap,
-			  SY7636A_REG_TERMISTOR_READOUT, &reg_val);
+	u8 buf[2];
+	int ret;
+
+	/*
+	 * The thermistor is sampled while ON_OFF is set, but the first sample
+	 * is only ready after the ADC sampling and conversion time (ADC_SPL +
+	 * ADC_DEL in the datasheet); until then it holds its reset value, 0.
+	 * PG is only set once all rails are up, after the first sample, so
+	 * read it in the same transfer and report the temperature only while
+	 * it is set.
+	 *
+	 * With ON_OFF set but PG low (rails still ramping up, or a fault), no
+	 * temperature is reported even if one may be available. That is
+	 * accepted: the display driver reads the temperature only while it
+	 * holds the rails on, after power good.
+	 */
+	ret = regmap_bulk_read(regmap, SY7636A_REG_FAULT_FLAG, buf, sizeof(buf));
 	if (ret)
 		return ret;
 
-	*temp = reg_val * 1000;
+	if (!(buf[0] & SY7636A_FAULT_FLAG_PG))
+		return -ENODATA;
+
+	*temp = (s8)buf[1] * 1000;
 
 	return 0;
 }
@@ -72,10 +89,6 @@ static int sy7636a_sensor_probe(struct auxiliary_device *adev,
 	if (!regmap)
 		return -ENODEV;
 
-	err = devm_regulator_get_enable(&adev->dev, "vcom");
-	if (err)
-		return err;
-
 	hwmon_dev = devm_hwmon_device_register_with_info(&adev->dev,
 							 "sy7636a_temperature", regmap,
 							 &sy7636a_chip_info, NULL);
-- 
2.52.0

Re: [PATCH v4 1/2] hwmon: sy7636a: read the temperature only while the rails are on

[sashiko-bot]

> The driver enables VCOM at probe, which keeps the panel's high voltage
> rails on for good. Read the temperature only while the rails are on, when
> the chip samples it, and return -ENODATA otherwise. Read power good with
> it in one transfer, so the value can not be from before the first sample
> or after the rails went off.
> 
> Signed-off-by: Pablo Mazzini <pmazzini@gmail.com>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261112205228.42630-1-pmazzini@gmail.com?part=1