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

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Message-ID: <20240325131605.6607b778@aktux>
Date: Mon, 25 Mar 2024 13:16:05 +0100
From: Andreas Kemnade <andreas@...nade.info>
To: Matti Vaittinen <mazziesaccount@...il.com>
Cc: lee@...nel.org, robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
 conor+dt@...nel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, imx@...ts.linux.dev
Subject: Re: [RFC PATCH 2/2] mfd: rohm-bd71828: Add power off functionality

On Mon, 25 Mar 2024 13:31:15 +0200
Matti Vaittinen <mazziesaccount@...il.com> wrote:

> 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...
> 
which btw: contains this interesting snippet (output from fdtdump)
  bd71828-i2c@4b {
                    reg = <0x0000004b>;
                    compatible = "rohm,bd71828";
                    gpio_int = <0x00000008 0x00000013 0x00000001>;
                    gpio_wdogb = <0x00000039 0x00000018 0x00000001>;
                    #address-cells = <0x00000001>;
                    #size-cells = <0x00000000>;
                    pmic@4b {
                        compatible = "rohm,bd71828";
             	        regulators {
                        	BUCK1 {
                            		regulator-name = "buck1";


and to make it work since basically no regulators are registered 
instead just some regmap_write()s are done to configure something
in probe(). It is a pitfall to think that the information below pmic@4b
is used, especially since it is not that obvious in the source.

> 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@...nade.info>
> > ---
> >   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.

well, so just check in bootloader what the reset reason is and check if
there is anything odd.

> I am unsure why i2c_smbus_write_byte_data() and 
> not regmap()?
> 
regmap involves mutex_lock() and we are not allowed to sleep here.

> > +	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.
> 
so maybe something to prevent power on by just plugging a usb cable? Will
experiment a bit with it.

> > +	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.
> 
I will to so. That will also remove the need for all those delays.

> > +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?
> 
oh, yes, that is not correct.

Regards,
Andreas