linux-kernel - Re: [PATCH 3/5] iio: inv_mpu6050: Check WHO_AM

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Date:	Mon, 25 Apr 2016 14:17:59 +0300
From:	Crestez Dan Leonard <leonard.crestez@...el.com>
To:	Jonathan Cameron <jic23@...nel.org>, linux-iio@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald-Stadler <pmeerw@...erw.net>,
	Daniel Baluta <daniel.baluta@...el.com>
Subject: Re: [PATCH 3/5] iio: inv_mpu6050: Check WHO_AM_I register on probe

On 04/24/2016 02:14 PM, Jonathan Cameron wrote:
> On 20/04/16 14:15, Crestez Dan Leonard wrote:
>> This can be used to distinguish mpu6500. This is a warning rather than
>> an error because the differences are mostly irrelevant and it's nice to
>> avoid breaking users with slightly incorrect ACPI/DT.
>>
>> Signed-off-by: Crestez Dan Leonard <leonard.crestez@...el.com>
> Would we be better off fixing their configuration though by using the right part
> if we can identify it?  So if wrong, maybe we should search the info table to 
> figure out what it is?  I'm not certain on this though as then we are trying to
> deal with unknown future cases - maybe what you have here is the best balance.

I'm not sure about that. One issue is that 6000/6050/9150 have the same
WHOAMI value and can't be distinguished this way. They also seem to
identical interfaces. Models MPU6500 and MPU9250 report different WHOAMI
values.

Changing chip_type based on the WHOAMI would require some additional
refactoring. Placing that in a separate patch might be worthwhile anyway.

>> +#define INV_MPU6050_REG_WHOAMI			117
>> +
>> +#define INV_MPU6000_WHOAMI_VALUE		0x68
>> +#define INV_MPU6050_WHOAMI_VALUE		0x68
>> +#define INV_MPU6500_WHOAMI_VALUE		0x70