Re: [RFC PATCH 2/2] mfd: rohm-bd71828: Add power off functionality

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On 3/24/24 22:12, Andreas Kemnade wrote:
Since the chip can power off the system, add the corresponding
functionality.
Based on https://github.com/kobolabs/Kobo-Reader/raw/master/hw/imx6sll-clara2e/kernel.tar.bz2
No information source about the magic numbers found.

Oh, interesting repository :) Thanks for linking to it! I didn't know someone had reworked this driver...

I have access to the data-sheets so I also have some pieces of information. I hope I can clarify part of the puzzle. Unfortunately I have no information about the magic delays. I guess I could try asking though.

Oh, it seems to me this handler is only working on BD71828, not on BD71815. So, it should be tied to the ROHM_CHIP_TYPE_BD71828.

Signed-off-by: Andreas Kemnade <andreas@xxxxxxxxxxxx>
---
  drivers/mfd/rohm-bd71828.c | 31 ++++++++++++++++++++++++++++++-
  1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/drivers/mfd/rohm-bd71828.c b/drivers/mfd/rohm-bd71828.c
index 594718f7e8e1..5a55aa3620d0 100644
--- a/drivers/mfd/rohm-bd71828.c
+++ b/drivers/mfd/rohm-bd71828.c
@@ -464,6 +464,24 @@ static int set_clk_mode(struct device *dev, struct regmap *regmap,
  				  OUT32K_MODE_CMOS);
  }
+static struct i2c_client *bd71828_dev;

I'm not sure why to store pointer to the device and not a pointer to the regmap?

+static void bd71828_power_off(void)
+{
+	i2c_smbus_write_byte_data(bd71828_dev, 0x03, 0xff);

0x03 is a "reset reason" - register. Spec I have states that the register should clear when a reset occurs - but it also says the bits are "write '1' to clear". So, for some reason(?), this clears the previous reset reason. I am unsure why i2c_smbus_write_byte_data() and not regmap()?

+	mdelay(500);
+	i2c_smbus_write_byte_data(bd71828_dev, BD71828_REG_INT_DCIN2, 0x02);

This clears the DCIN monitoring status bit from the IRQ status register. I don't understand the purpose though.

+	mdelay(500);
+	while (true) {
+		i2c_smbus_write_byte_data(bd71828_dev, BD71828_REG_PS_CTRL_1, 0x02);

This write to PS_CTRL_1 initiates a state transition. 0x2 equals to HBNT state. Eg, in usual cases this should be a start of the power-off sequence.

+		mdelay(500);
+	}
+}

If you have the hardware to test this on, then it'd be great to see if clearing the reset reason and IRQ status could be dropped. I can't immediately think of a reason for those.

+static void bd71828_remove_poweroff(void *data)
+{
+	bd71828_dev = NULL;

This does not smell correct to me. Should we remove the bd71828_power_off() from the pm_power_off instead?

+}
+
  static int bd71828_i2c_probe(struct i2c_client *i2c)
  {
  	struct regmap_irq_chip_data *irq_data;
@@ -542,7 +560,18 @@ static int bd71828_i2c_probe(struct i2c_client *i2c)
  	ret = devm_mfd_add_devices(&i2c->dev, PLATFORM_DEVID_AUTO, mfd, cells,
  				   NULL, 0, regmap_irq_get_domain(irq_data));
  	if (ret)
-		dev_err_probe(&i2c->dev, ret, "Failed to create subdevices\n");
+		return	dev_err_probe(&i2c->dev, ret, "Failed to create subdevices\n");
+
+	if (of_device_is_system_power_controller(i2c->dev.of_node)) {
+		if (!pm_power_off) {
+			bd71828_dev = i2c;
+			pm_power_off = bd71828_power_off;
+			ret = devm_add_action_or_reset(&i2c->dev,
+						       bd71828_remove_poweroff,
+						       NULL);
+		} else
+			dev_warn(&i2c->dev, "Poweroff callback already assigned\n");
+	}
return ret;
  }

Thanks for doing the digging Andreas! I think supporting the power-off for devices using this PMIC is nice!

Yours,
	-- Matti

--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

~~ When things go utterly wrong vim users can always type :help! ~~





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