Re: [PATCH 3/3] iio: temperature: ltc2983: support more parts

[Cosmin Tanislav]

On 10/14/22 18:44, Jonathan Cameron wrote:
> On Fri, 14 Oct 2022 15:37:24 +0300
> Cosmin Tanislav <demonsingur@xxxxxxxxx> wrote:
>
> > From: Cosmin Tanislav <cosmin.tanislav@xxxxxxxxxx>
> >
> > Add support for the following parts:
> >   * LTC2984
> >   * LTC2986
> >   * LTM2985
> >
> > The LTC2984 is a variant of the LTC2983 with EEPROM.
> > The LTC2986 is a variant of the LTC2983 with only 10 channels,
> > EEPROM and support for active analog temperature sensors.
> > The LTM2985 is software-compatible with the LTC2986.
> >
> > Signed-off-by: Cosmin Tanislav <cosmin.tanislav@xxxxxxxxxx>
>
> ...
>
> Hi Cosmin,
>
> Looks good except, I think we are still in the position that
> regmap for spi doesn't guarantee to bounce buffer the bulk accesses
> (last time I checked it actually did do so, but before that it didn't
> and there are obvious optimizations to take it back to not doing so -
> IRC Mark Brown's answer was we shouldn't rely on it..)
>
> Anyhow, the existing driver has instances of this so its no worse
> but we should really clean those up.
>
> Jonathan

I can submit another patch for it. Although I'm pretty sure that
SPI regmap implementation doesn't need DMA safe access for it,
as I checked when I wrote the code.

> >   
> > +static int ltc2983_eeprom_cmd(struct ltc2983_data *st, unsigned int cmd,
> > +			      unsigned int wait_time, unsigned int status_reg,
> > +			      unsigned long status_fail_mask)
> > +{
> > +	__be32 bval = cpu_to_be32(LTC2983_EEPROM_KEY);
> > +	unsigned long time;
> > +	unsigned int val;
> > +	int ret;
> > +
> > +	ret = regmap_bulk_write(st->regmap, LTC2983_EEPROM_KEY_REG, &bval,
> > +				sizeof(bval));
>
> SPI device and I was clearly dozing on existing driver but normally
> we avoid assuming that regmap will always use a bounce buffer for bulk
> accessors. Hence this should be a DMA safe buffer.
>
>
> > +	if (ret)
> > +		return ret;
> > +
> > +	reinit_completion(&st->completion);
> > +
> > +	ret = regmap_write(st->regmap, LTC2983_STATUS_REG,
> > +			   LTC2983_STATUS_START(true) | cmd);
> > +	if (ret)
> > +		return ret;
> > +
> > +	time = wait_for_completion_timeout(&st->completion,
> > +					   msecs_to_jiffies(wait_time));
> > +	if (!time) {
> > +		dev_err(&st->spi->dev, "EEPROM command timed out\n");
> > +		return -ETIMEDOUT;
> > +	}
> > +
> > +	ret = regmap_read(st->regmap, status_reg, &val);
> > +	if (ret)
> > +		return ret;
> > +
> > +	if (val & status_fail_mask) {
> > +		dev_err(&st->spi->dev, "EEPROM command failed: 0x%02X\n", val);
> > +		return -EINVAL;
> > +	}
> > +
> > +	return 0;
> > +}
> > +