Re: [PATCH 7/8] iio: imu: inv_mpu6050: align buffer for timestamp

[Jean-Baptiste Maneyrol]

On Thu, 17 Apr 2025 19:46:00, Jonathan Cameron wrote:
> On Thu, 17 Apr 2025 20:00:05 +0300
> Andy Shevchenko <andy@xxxxxxxxxx> wrote:
> 
> > On Thu, Apr 17, 2025 at 11:52:39AM -0500, David Lechner wrote:
> > > Align the buffer used with iio_push_to_buffers_with_timestamp() to
> > > ensure the s64 timestamp is aligned to 8 bytes.  
> > 
> > Same question as per previous patch.
> > 
> In this case I don't think we know the position of the timestamp
> so a structure would be misleading.
> 
> The comment above the define certainly suggests it is variable..

I confirm timestamp position is changing depending on channels enabled. It
can be at address 8, 16 or 24.

If there is only 1 sensor enabled (6 bytes of data), timestamp is at address
8. 2 sensors (12 bytes of data), timestamp will be at address 16. 3 sensors
for MPU-9xxx (19 bytes of data), timestamp will be at address 24.

If the buffer is aligned on 8 bytes, it will always work without any problem.

> 
> /*
>  * Maximum of 6 + 6 + 2 + 7 (for MPU9x50) = 21 round up to 24 and plus 8.
>  * May be less if fewer channels are enabled, as long as the timestamp
>  * remains 8 byte aligned
>  */
> #define INV_MPU6050_OUTPUT_DATA_SIZE         32

Thanks,
JB