linux-kernel - Re: [PATCH v2 4/6] iio: pressure: Simplify and make more clear temperature readings

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Date: Fri, 15 Mar 2024 10:05:26 +0100
From: Vasileios Amoiridis <vassilisamir@...il.com>
To: Angel Iglesias <ang.iglesiasg@...il.com>
Cc: Vasileios Amoiridis <vassilisamir@...il.com>,
	Jonathan Cameron <jic23@...nel.org>, lars@...afoo.de,
	andriy.shevchenko@...ux.intel.com, mazziesaccount@...il.com,
	ak@...klinger.de, petre.rodan@...dimension.ro,
	linus.walleij@...aro.org, phil@...pberrypi.com, 579lpy@...il.com,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/6] iio: pressure: Simplify and make more clear
 temperature readings

On Fri, Mar 15, 2024 at 12:22:50AM +0100, Angel Iglesias wrote:
> On Thu, 2024-03-14 at 21:17 +0100, Vasileios Amoiridis wrote:
> > On Thu, Mar 14, 2024 at 03:09:59PM +0000, Jonathan Cameron wrote:
> > > On Wed, 13 Mar 2024 18:40:05 +0100
> > > Vasileios Amoiridis <vassilisamir@...il.com> wrote:
> > > 
> > > > The read_press/read_humid functions need the updated t_fine value
> > > > in order to calculate the current pressure/humidity. Temperature
> > > > reads should be removed from the read_press/read_humid functions
> > > > and should be placed in the oneshot captures before the pressure
> > > > and humidity reads. This makes the code more intuitive.
> > > > 
> > > > Signed-off-by: Vasileios Amoiridis <vassilisamir@...il.com>
> > > 
> > > To me this makes the use of these calls less obvious than they were
> > > previously.  The calls are made close to where t_fine is used and
> > > don't have to go via the indirection of chip_info.
> > > 
> > > So I disagree. I think this change makes the code a lot less
> > > clear.
> > > 
> > 
> > This was mainly driven by the fact that I wanted to avoid reading
> > the temperature 3 times in case temp, press and humid are enabled
> > and there are consecutive buffer readings. But thank you for the
> > proposal I really appreciate it!
> > 
> 
> Hi, just a side note reflecting on this. Depending on your sampling frequency
> and registers data shadowing, to avoid compensating with different samples
> between readings, we should be doing burst readings to get a bundle of the
> temperature+pressure and/or humidity.
> On the bmp/bme280 and bmp380 this can be done as registers are contiguous on the
> memory. On the bmp580 this is not a problem as the values are already
> compensated, you`ll get always the latest reading.
> 
> Kind regard,
> Angel

Hi Angel,

Thank you for pointing this out! Indeed that's true but I noticed that this is not
the case for the BMP{085/180} devices. I just feel that some changes might make
data acquisition/processing faster for a device (like the one you proposed) but
it might make the code much more unreadable and unmaintanable. I will try and
see if something could be done in that sense but I feel that keeping it simple will
be good for everyone!

Cheers,
Vasilis