Date:   Mon, 15 Aug 2022 08:59:03 -0500
From:   Eddie James <eajames@...ux.ibm.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     linux-iio <linux-iio@...r.kernel.org>,
        Jonathan Cameron <jic23@...nel.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 2/2] iio: pressure: dps310: Reset chip if MEAS_CFG is
 corrupt


On 8/12/22 17:13, Andy Shevchenko wrote:
> On Wed, Aug 10, 2022 at 12:12 AM Eddie James <eajames@...ux.ibm.com> wrote:
>> Corruption of the MEAS_CFG register has been observed soon after
>> system boot. In order to recover this scenario, check MEAS_CFG if
>> measurement isn't ready, and if it's incorrect, reset the DPS310
>> and execute the startup procedure.
> Looks like both patches miss the Fixes tag. Can you add them?


Well this isn't really a software fix - there's no identifiable bug in 
the driver. Just trying to recover the chip in this observed mystery 
scenario.


>
> ...
>
>> +/*
>> + * Called with lock held. Returns a negative value on error, a positive value
>> + * when the device is not ready, and zero when the device is ready.
>> + */
>> +static int dps310_check_reset_meas_cfg(struct dps310_data *data, int ready_bit)
>> +{
>> +       int meas_cfg;
>> +       int rc = regmap_read(data->regmap, DPS310_MEAS_CFG, &meas_cfg);
>> +
>> +       if (rc < 0)
>> +               return rc;
> Please, split definition and assignment.


Ack.


>
>> +       /* Device is ready, proceed to measurement */
>> +       if (meas_cfg & ready_bit)
>> +               return 0;
>> +
>> +       /* Device is OK, just not ready */
>> +       if (meas_cfg & (DPS310_PRS_EN | DPS310_TEMP_EN | DPS310_BACKGROUND))
>> +               return 1;
>> +
>> +       /* DPS310 register state corrupt, better start from scratch */
>> +       rc = regmap_write(data->regmap, DPS310_RESET, DPS310_RESET_MAGIC);
>> +       if (rc < 0)
>> +               return rc;
>> +
>> +       /* Wait for device chip access: 2.5ms in specification */
>> +       usleep_range(2500, 12000);
>> +
>> +       /* Reinitialize the chip */
>> +       rc = dps310_startup(data);
>> +       if (rc)
>> +               return rc;
>> +
>> +       dev_info(&data->client->dev,
>> +                "recovered from corrupted MEAS_CFG=%02x\n", meas_cfg);
>> +       return 1;
>> +}
>> +
>>   static int dps310_read_pres_raw(struct dps310_data *data)
>>   {
>>          int rc;
>> @@ -405,16 +443,26 @@ static int dps310_read_pres_raw(struct dps310_data *data)
>>          if (mutex_lock_interruptible(&data->lock))
>>                  return -EINTR;
>>
>> -       rate = dps310_get_pres_samp_freq(data);
>> -       timeout = DPS310_POLL_TIMEOUT_US(rate);
>> -
>> -       /* Poll for sensor readiness; base the timeout upon the sample rate. */
>> -       rc = regmap_read_poll_timeout(data->regmap, DPS310_MEAS_CFG, ready,
>> -                                     ready & DPS310_PRS_RDY,
>> -                                     DPS310_POLL_SLEEP_US(timeout), timeout);
>> -       if (rc)
>> +       rc = dps310_check_reset_meas_cfg(data, DPS310_PRS_RDY);
>> +       if (rc < 0)
>>                  goto done;
>>
>> +       if (rc > 0) {
>> +               rate = dps310_get_pres_samp_freq(data);
>> +               timeout = DPS310_POLL_TIMEOUT_US(rate);
>> +
>> +               /*
>> +                * Poll for sensor readiness; base the timeout upon the sample
>> +                * rate.
>> +                */
>> +               rc = regmap_read_poll_timeout(data->regmap, DPS310_MEAS_CFG,
>> +                                             ready, ready & DPS310_PRS_RDY,
>> +                                             DPS310_POLL_SLEEP_US(timeout),
>> +                                             timeout);
>> +               if (rc)
>> +                       goto done;
>> +       }
> If you split the condition body to a helper, it can be rewritten like
> (also note special definition for positive returned numbers):
>
>    rc = ..._reset_meas_cfg(...);
>    if (rc  == DPS310_MEAS_NOT_READY)
>      rc = ..._new_helper_func(...);
>    if (rc)
>      goto done;
>
> and looking at this it might be worth considering calling that
> conditional in the middle in the _reset_meas_cfg(), so the latter will
> return either 0 or negative error code.


To be honest that looks more complicated than the way it is now? And I 
don't think I can make it common between the temp and pressure without 
some complicated macro business.


>
>> +       rc = dps310_check_reset_meas_cfg(data, DPS310_TMP_RDY);
>>          if (rc < 0)
>>                  goto done;
>>
>> +       if (rc > 0) {
>> +               rate = dps310_get_temp_samp_freq(data);
> Okay, I see this function is different, but still you may realize a
> helper from below and something like above suggestion can still be
> achieved.
>
>> +               timeout = DPS310_POLL_TIMEOUT_US(rate);
>> +
>> +               /*
>> +                * Poll for sensor readiness; base the timeout upon the sample
>> +                * rate.
>> +                */
>> +               rc = regmap_read_poll_timeout(data->regmap, DPS310_MEAS_CFG,
>> +                                             ready, ready & DPS310_TMP_RDY,
>> +                                             DPS310_POLL_SLEEP_US(timeout),
>> +                                             timeout);
>> +               if (rc < 0)
> Why out of a sudden ' < 0'?


Good point, I'll fix that.


>
>> +                       goto done;
>> +       }
> As per above.
>
>>          rc = dps310_read_temp_ready(data);
>

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