linux-kernel - Re: [PATCH v4 2/2] power: supply: add support for MAX1720x standalone fuel gauge

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Date: Wed, 19 Jun 2024 18:09:48 +0200
From: Dimitri Fedrau <dima.fedrau@...il.com>
To: Sebastian Reichel <sebastian.reichel@...labora.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-pm@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Thomas Weißschuh <thomas@...ch.de>
Subject: Re: [PATCH v4 2/2] power: supply: add support for MAX1720x
 standalone fuel gauge

Hi Sebastian,

Am Wed, Jun 19, 2024 at 05:30:27PM +0200 schrieb Sebastian Reichel:
> Hi,
> 
> On Wed, Jun 19, 2024 at 08:14:07AM GMT, Dimitri Fedrau wrote:
> > Am Wed, Jun 19, 2024 at 01:19:32AM +0200 schrieb Sebastian Reichel:
> > > On Mon, Jun 17, 2024 at 08:45:04PM GMT, Dimitri Fedrau wrote:
> > > > The MAX17201 monitors a single cell pack. The MAX17205 monitors and
> > > > balances a 2S or 3S pack or monitors a multiple-series cell pack. Both
> > > > devices use a I2C interface.
> > > > 
> > > > Signed-off-by: Dimitri Fedrau <dima.fedrau@...il.com>
> > > > ---
> > > 
> > > [...]
> > > 
> > > > +static int max1720x_read_word_data_nvmem(struct i2c_client *ancillary, u8 addr)
> > > > +{
> > > > +	u8 rx[2];
> > > > +	struct i2c_msg msgs[] = {
> > > > +		{
> > > > +			.addr = ancillary->addr,
> > > > +			.flags = 0,
> > > > +			.len = 1,
> > > > +			.buf = &addr,
> > > > +		},
> > > > +		{
> > > > +			.addr = ancillary->addr,
> > > > +			.flags = I2C_M_RD,
> > > > +			.len = 2,
> > > > +			.buf = &rx[0],
> > > > +		},
> > > > +	};
> > > > +	int ret;
> > > > +
> > > > +	ret = i2c_transfer(ancillary->adapter, msgs, ARRAY_SIZE(msgs));
> > > > +	if (ret != ARRAY_SIZE(msgs))
> > > > +		return ret < 0 ? ret : -EIO;
> > > > +
> > > > +	return get_unaligned_le16(&rx[0]);
> > > > +}
> > > 
> > > Have you tried using i2c_smbus_read_word_data(ancillary, addr)
> > > instead of the above?
> > >
> > Yes, I did and it worked. Used it in V3 and changed it due to review
> > comments by Thomas which make sense to me. I don't have any preference on
> > this. Should I change it back ?
> 
> Using the smbus function makes the driver work with a pure SMBus
> adapter and keeps it working with I2C adapters through the SMBus
> "emulation". By using the open coded version we have more code and
> the driver does not work with pure SMBus adapters.
> 
> So I see no reason why the open coded version should be used. Note,
> that regmap also uses i2c_smbus_read_word_data() internally for your
> configuration of the non-ancillary device.
> 

Thanks for the explanation, will switch to i2c_smbus_read_word_data in
the next version.

Dimitri