linux-kernel - Re: [PATCH v2 2/3] iio: dps310: Temperature measurement errata

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Message-ID: <CAJCx=gk3EwF_CTjVm=Ktx408iqcYUgZCSbZABXBSuGjfAjwXQw@mail.gmail.com>
Date:   Fri, 10 May 2019 10:21:02 +0800
From:   Matt Ranostay <matt.ranostay@...sulko.com>
To:     Eddie James <eajames@...ux.vnet.ibm.com>
Cc:     Eddie James <eajames@...ux.ibm.com>,
        "open list:IIO SUBSYSTEM AND DRIVERS" <linux-iio@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>, joel@....id.au,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Hartmut Knaack <knaack.h@....de>,
        Jonathan Cameron <jic23@...nel.org>,
        Christopher Bostic <cbostic@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 2/3] iio: dps310: Temperature measurement errata

On Thu, May 9, 2019 at 11:17 PM Eddie James <eajames@...ux.vnet.ibm.com> wrote:
>
>
> On 5/8/19 10:09 PM, Matt Ranostay wrote:
> > On Thu, May 9, 2019 at 3:36 AM Eddie James <eajames@...ux.ibm.com> wrote:
> >> From: Christopher Bostic <cbostic@...ux.vnet.ibm.com>
> >>
> >> Add a manufacturer's suggested workaround to deal with early revisions
> >> of chip that don't indicate correct temperature. Readings can be in the
> >> ~60C range when they should be in the ~20's.
> >>
> >> Signed-off-by: Christopher Bostic <cbostic@...ux.vnet.ibm.com>
> >> Signed-off-by: Joel Stanley <joel@....id.au>
> >> Signed-off-by: Eddie James <eajames@...ux.ibm.com>
> >> ---
> >>   drivers/iio/pressure/dps310.c | 51 ++++++++++++++++++++++++++++++++++++++++++-
> >>   1 file changed, 50 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/iio/pressure/dps310.c b/drivers/iio/pressure/dps310.c
> >> index 7afaa88..c42808e 100644
> >> --- a/drivers/iio/pressure/dps310.c
> >> +++ b/drivers/iio/pressure/dps310.c
> >> @@ -221,6 +221,9 @@ static bool dps310_is_writeable_reg(struct device *dev, unsigned int reg)
> >>          case DPS310_MEAS_CFG:
> >>          case DPS310_CFG_REG:
> >>          case DPS310_RESET:
> >> +       case 0x0e:
> >> +       case 0x0f:
> >> +       case 0x62:
> > What is with the magic values? Are they not documented to what they
> > are, and hence not defining enum values for them?
> >
> > - Matt
>
>
> Thats correct. These don't show up in the data sheet so I left them as
> raw values. Chris, do you know what the source for these values was?

Please at least make a comment in the code stating as much.

- Matt
>
> Thanks,
>
> Eddie
>
>
> >
> >>                  return true;
> >>          default:
> >>                  return false;
> >> @@ -237,6 +240,7 @@ static bool dps310_is_volatile_reg(struct device *dev, unsigned int reg)
> >>          case DPS310_TMP_B1:
> >>          case DPS310_TMP_B2:
> >>          case DPS310_MEAS_CFG:
> >> +       case 0x32:
> >>                  return true;
> >>          default:
> >>                  return false;
> >> @@ -314,7 +318,7 @@ static int dps310_read_raw(struct iio_dev *iio,
> >>          .writeable_reg = dps310_is_writeable_reg,
> >>          .volatile_reg = dps310_is_volatile_reg,
> >>          .cache_type = REGCACHE_RBTREE,
> >> -       .max_register = 0x29,
> >> +       .max_register = 0x62,
> >>   };
> >>
> >>   static const struct iio_info dps310_info = {
> >> @@ -322,6 +326,47 @@ static int dps310_read_raw(struct iio_dev *iio,
> >>          .write_raw = dps310_write_raw,
> >>   };
> >>
> >> +/*
> >> + * Some verions of chip will read temperatures in the ~60C range when
> >> + * its actually ~20C. This is the manufacturer recommended workaround
> >> + * to correct the issue.
> >> + */
> >> +static int dps310_temp_workaround(struct dps310_data *data)
> >> +{
> >> +       int r, reg;
> >> +
> >> +       r = regmap_read(data->regmap, 0x32, &reg);
> >> +       if (r < 0)
> >> +               return r;
> >> +
> >> +       /*
> >> +        * If bit 1 is set then the device is okay, and the workaround does not
> >> +        * need to be applied
> >> +        */
> >> +       if (reg & BIT(1))
> >> +               return 0;
> >> +
> >> +       r = regmap_write(data->regmap, 0x0e, 0xA5);
> >> +       if (r < 0)
> >> +               return r;
> >> +
> >> +       r = regmap_write(data->regmap, 0x0f, 0x96);
> >> +       if (r < 0)
> >> +               return r;
> >> +
> >> +       r = regmap_write(data->regmap, 0x62, 0x02);
> >> +       if (r < 0)
> >> +               return r;
> >> +
> >> +       r = regmap_write(data->regmap, 0x0e, 0x00);
> >> +       if (r < 0)
> >> +               return r;
> >> +
> >> +       r = regmap_write(data->regmap, 0x0f, 0x00);
> >> +
> >> +       return r;
> >> +}
> >> +
> >>   static int dps310_probe(struct i2c_client *client,
> >>                          const struct i2c_device_id *id)
> >>   {
> >> @@ -383,6 +428,10 @@ static int dps310_probe(struct i2c_client *client,
> >>          if (r < 0)
> >>                  goto err;
> >>
> >> +       r = dps310_temp_workaround(data);
> >> +       if (r < 0)
> >> +               return r;
> >> +
> >>          r = devm_iio_device_register(&client->dev, iio);
> >>          if (r)
> >>                  goto err;
> >> --
> >> 1.8.3.1
> >>
>