linux-kernel - Re: [PATCH v2 1/3] iio: magnetometer: ak8975: Fix reading for ak099xx sensors

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Message-ID: <96c2bcfbebc9e6d97d97f32aec9249db@mainlining.org>
Date: Wed, 07 Aug 2024 17:15:46 +0200
From: barnabas.czeman@...nlining.org
To: Jonathan Cameron <jic23@...nel.org>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Jonathan Albrieux <jonathan.albrieux@...il.com>,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, linux@...nlining.org
Subject: Re: [PATCH v2 1/3] iio: magnetometer: ak8975: Fix reading for ak099xx
 sensors

On 2024-08-06 18:19, Jonathan Cameron wrote:
> On Tue, 06 Aug 2024 08:10:18 +0200
> Barnabás Czémán <barnabas.czeman@...nlining.org> wrote:
> 
> Hi Barnabás,
> 
> Welcome to IIO.
> 
>> ST2 register read should be placed after read measurment data,
>> because it will get correct values after it.
> 
> What is the user visible result of this? Do we detect errors when none
> are there?  Do we have a datasheet reference for the status being
> update on the read command, not after the trigger?
>> 
> Needs a Fixes tag to let us know how far to backport the fix.
> 
> A few comments inline.
> 
>> Signed-off-by: Barnabás Czémán <barnabas.czeman@...nlining.org>
>> ---
>>  drivers/iio/magnetometer/ak8975.c | 31 
>> +++++++++++++++----------------
>>  1 file changed, 15 insertions(+), 16 deletions(-)
>> 
>> diff --git a/drivers/iio/magnetometer/ak8975.c 
>> b/drivers/iio/magnetometer/ak8975.c
>> index dd466c5fa621..925d76062b3e 100644
>> --- a/drivers/iio/magnetometer/ak8975.c
>> +++ b/drivers/iio/magnetometer/ak8975.c
>> @@ -692,22 +692,7 @@ static int ak8975_start_read_axis(struct 
>> ak8975_data *data,
>>  	if (ret < 0)
>>  		return ret;
>> 
>> -	/* This will be executed only for non-interrupt based waiting case 
>> */
>> -	if (ret & data->def->ctrl_masks[ST1_DRDY]) {
>> -		ret = i2c_smbus_read_byte_data(client,
>> -					       data->def->ctrl_regs[ST2]);
>> -		if (ret < 0) {
>> -			dev_err(&client->dev, "Error in reading ST2\n");
>> -			return ret;
>> -		}
>> -		if (ret & (data->def->ctrl_masks[ST2_DERR] |
>> -			   data->def->ctrl_masks[ST2_HOFL])) {
>> -			dev_err(&client->dev, "ST2 status error 0x%x\n", ret);
>> -			return -EINVAL;
>> -		}
>> -	}
>> -
> This completely removes the check from the _fill_buffer() path
> 
>> -	return 0;
>> +	return !(ret & data->def->ctrl_masks[ST1_DRDY]);
> returning a positive value here is unusual enough you should add a 
> comment for
> the function + use that return value.
> 
>>  }
>> 
>>  /* Retrieve raw flux value for one of the x, y, or z axis.  */
>> @@ -731,6 +716,20 @@ static int ak8975_read_axis(struct iio_dev 
>> *indio_dev, int index, int *val)
>>  	ret = i2c_smbus_read_i2c_block_data_or_emulated(
>>  			client, def->data_regs[index],
>>  			sizeof(rval), (u8*)&rval);
> No longer gated on ret & data->def->ctrl_masks[ST1_DRDY] which seems 
> unintentional.
It is checked exactly before the measurement data read, it is the return 
value of ak8975_start_read_axis.
The read section should be ST1 -> measurement -> ST2, exactly the same 
can be found in the datasheets.
> 
> Still need a check on ret here.
> 
>> +	ret = i2c_smbus_read_byte_data(client,
>> +				       data->def->ctrl_regs[ST2]);
>> +	if (ret < 0) {
>> +		dev_err(&client->dev, "Error in reading ST2\n");
>> +		goto exit;
>> +	}
>> +
>> +	if (ret & (data->def->ctrl_masks[ST2_DERR] |
>> +		   data->def->ctrl_masks[ST2_HOFL])) {
>> +		dev_err(&client->dev, "ST2 status error 0x%x\n", ret);
>> +		ret = -EINVAL;
>> +		goto exit;
>> +	}
>> +
>>  	if (ret < 0)
>>  		goto exit;
> 
> And this one ends up redundant I think which suggests to me the
> code is inserted a few lines early.
> 
>> 
>>