linux-kernel - Re: [PATCH 1/2] hwmon: (pmbus/isl68137) add debugfs config and black box endpoints

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Message-ID: <20200421214917.GA28170@raspberrypi>
Date:   Tue, 21 Apr 2020 16:49:17 -0500
From:   Grant Peltier <grantpeltier93@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        adam.vaughn.xh@...esas.com, grant.peltier.jg@...esas.com
Subject: Re: [PATCH 1/2] hwmon: (pmbus/isl68137) add debugfs config and black
 box endpoints

On Tue, Apr 21, 2020 at 11:58:51AM -0700, Guenter Roeck wrote:
> Normally this is emulated for such controllers. I don't recall seeing
> such a need before. The code below duplicates similar code in
> i2c_smbus_xfer_emulated(), which is much more sophisticated.
> Are you sure this is needed ? Can you point me to an affected
> controller ?
> 
> > +static s32 raa_smbus_read40(const struct i2c_client *client, u8 command,
> > +			    unsigned char *data)
> > +{
> > +	int status;
> > +	unsigned char msgbuf[1];
> > +	struct i2c_msg msg[2] = {
> > +		{
> > +			.addr = client->addr,
> > +			.flags = client->flags,
> > +			.len = 1,
> > +			.buf = msgbuf,
> > +		},
> > +		{
> > +			.addr = client->addr,
> > +			.flags = client->flags | I2C_M_RD,
> > +			.len = 5,
> > +			.buf = data,
> > +		},
> > +	};
> > +
> > +	msgbuf[0] = command;
> > +	status = i2c_transfer(client->adapter, msg, 2);
> > +	if (status != 2)
> > +		return status;
> 
> i2c_transfer() can return 1 if only one of the two messages was sent.
> 
> > +	return 0;
> > +}
I have been using BCM2835 for most of my testing. I originally tried using
i2c_smbus_read_block_data() but that was returning errors. However, from your
email, I went back and tried i2c_smbus_read_i2c_block_data() and that appears
to be working so I will switch to that instead.

> > +
> > +/**
> > + * Helper function required since linux SMBus implementation does not currently
> > + * (v5.6) support the SMBus 3.0 "Read 32" protocol
> > + */
> > +static s32 raa_dmpvr2_smbus_read32(const struct i2c_client *client, u8 command,
> > +				   unsigned char *data)
> > +{
> > +	int status;
> > +	unsigned char msgbuf[1];
> > +	struct i2c_msg msg[2] = {
> > +		{
> > +			.addr = client->addr,
> > +			.flags = client->flags,
> > +			.len = 1,
> > +			.buf = msgbuf,
> > +		},
> > +		{
> > +			.addr = client->addr,
> > +			.flags = client->flags | I2C_M_RD,
> > +			.len = 4,
> > +			.buf = data,
> > +		},
> > +	};
> > +
> > +	msgbuf[0] = command;
> > +	status = i2c_transfer(client->adapter, msg, 2);
> > +	if (status != 2)
> > +		return status;
> > +	return 0;
> > +}
> 
> Maybe it would be worthwhile to consider implementing it ?
> 
I could add these functions to i2c-core-smbus instead if that is desired.
However, I am unsure if it would be proper to only partially update the SMBus
implementation to match the 3.0 spec. Is there perhaps a better forum to
discuss adding all of the 3.0 changes?