linux-kernel - Re: [PATCH v4 1/2] iio: pressure: dps310: Refactor startup procedure

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Date:   Sat, 20 Aug 2022 12:49:15 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Eddie James <eajames@...ux.ibm.com>,
        linux-iio <linux-iio@...r.kernel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Joel Stanley <joel@....id.au>
Subject: Re: [PATCH v4 1/2] iio: pressure: dps310: Refactor startup
 procedure

On Fri, 19 Aug 2022 12:42:00 +0300
Andy Shevchenko <andy.shevchenko@...il.com> wrote:

> On Mon, Aug 15, 2022 at 4:42 PM Eddie James <eajames@...ux.ibm.com> wrote:
> > On 8/12/22 17:03, Andy Shevchenko wrote:  
> > > On Wed, Aug 10, 2022 at 12:12 AM Eddie James <eajames@...ux.ibm.com> wrote:  
> 
> ...
> 
> > >> +       rc = regmap_write(data->regmap, 0x0e, 0xA5);
> > >> +       if (rc)
> > >> +               return rc;
> > >> +
> > >> +       rc = regmap_write(data->regmap, 0x0f, 0x96);
> > >> +       if (rc)
> > >> +               return rc;  
> > > This code already exists, but still want to ask, is it really
> > > byte-registers here and not be16/le16 one? In such a case perhaps bulk
> > > write can be used to reflect it better?  
> >
> > The temperature and pressure regs are 24 bits big endian, and all the
> > rest are 8 bits. I think the existing approach is best.  
> 
> It doesn't look like you got what I was meaning... Or I misunderstood
> what you said.
> 
> The code above writes two byte values to two sequential registers
> which make me think that they are 16-bit registers at offset 0x0e.

Given they are undocumented, this is guessing territory.
Probably best to just leave them as is.
You could do a bulk write on an array though as that implies
nothing about what's in the registers -just that they happen
to be next to each other.

> 
> ...
> 
> > >> +       rc = regmap_write(data->regmap, 0x0e, 0x00);
> > >> +       if (rc)
> > >> +               return rc;
> > >> +
> > >> +       return regmap_write(data->regmap, 0x0f, 0x00);  
> 
> Ditto.
>