Re: [PATCH v3.1 2/3] iio: chemical: Add Senseair Sunrise 006-0-007 driver

[Peter Rosin <peda@axentia.se>]

On 2021-09-06 01:03, Peter Rosin wrote:
> On 2021-09-05 12:04, Jonathan Cameron wrote:
>> On Tue, 31 Aug 2021 09:40:11 +0200
>> Jacopo Mondi <jacopo@jmondi.org> wrote:
>>
>>> Hi Jonathan,
>>>    two more clarification requests, sorry to bother :)
>> No problem.  First one: No idea +CC wolfram and i2c list.
>>>
>>> On Mon, Aug 30, 2021 at 06:11:17PM +0100, Jonathan Cameron wrote:
>>>> On Mon, 30 Aug 2021 18:20:51 +0200  
>>>>>>> +static int sunrise_write_word(struct sunrise_dev *sunrise, u8 reg, u16 data)
>>>>>>> +{
>>>>>>> +	__be16 be_data = cpu_to_be16(data);
>>>>>>> +	int ret;
>>>>>>> +
>>>>>>> +	sunrise_wakeup(sunrise);  
>>>>>>
>>>>>> Hmm. Technically there isn't anything stopping another user of the i2c bus sneaking in
>>>>>> between the wakeup and the following command.  That would make the device going back
>>>>>> to sleep a lot more likely.  I can't off the top of my head remember if regmap lets
>>>>>> you lock the bus.  If not, you'll have to use the underlying i2c bus locking functions.
>>>>>> https://elixir.bootlin.com/linux/latest/source/drivers/iio/temperature/mlx90614.c#L432
>>>>>> gives an example.

Forgot to mention, regmap does let you do that. See e.g.
drivers/media/dvb-frontends/rtl2830.c which wraps regmap_update_bits,
regmap_bulk_write and regmap_bulk_read within a local I2C segment
lock along with a special regmap_bus that does unlocked I2C trasfers.

I think the driver does this because it has an I2C gate that needs to
be opened with a regmap interaction that in turn needs to be back to
back with the "real" regmap access, or else the gate closes again.

Cheers,
Peter