linux-kernel - Re: [PATCH 06/14] iio: pressure: mprls0025pa: memset rx

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Message-ID: <aUZdb9R9BLMfBpLJ@sunspire.home.arpa>
Date: Sat, 20 Dec 2025 10:25:19 +0200
From: Petre Rodan <petre.rodan@...dimension.ro>
To: Marcelo Schmitt <marcelo.schmitt1@...il.com>
Cc: Jonathan Cameron <jic23@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>,
	Andreas Klinger <ak@...klinger.de>, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH 06/14] iio: pressure: mprls0025pa: memset rx_buf before
 reading new data


Hello,

On Sat, Dec 20, 2025 at 01:47:05AM -0300, Marcelo Schmitt wrote:
> On 12/18, Petre Rodan wrote:
> > Zero out input buffer before reading the new conversion.
> > Perform this operation in core instead of in the bus specific code.
> > 
> > Signed-off-by: Petre Rodan <petre.rodan@...dimension.ro>
> > ---
> >  drivers/iio/pressure/mprls0025pa.c     | 2 ++
> >  drivers/iio/pressure/mprls0025pa_i2c.c | 1 -
> >  2 files changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iio/pressure/mprls0025pa.c b/drivers/iio/pressure/mprls0025pa.c
> > index 00b1ff1e50a8..7cc8dd0d8476 100644
> > --- a/drivers/iio/pressure/mprls0025pa.c
> > +++ b/drivers/iio/pressure/mprls0025pa.c
> > @@ -16,6 +16,7 @@
> >  #include <linux/mod_devicetable.h>
> >  #include <linux/module.h>
> >  #include <linux/property.h>
> > +#include <linux/string.h>
> >  #include <linux/units.h>
> >  
> >  #include <linux/gpio/consumer.h>
> > @@ -239,6 +240,7 @@ static int mpr_read_pressure(struct mpr_data *data, s32 *press)
> >  		}
> >  	}
> >  
> > +	memset(data->rx_buf, 0, sizeof(data->rx_buf));
> This is unusual and I don't think it's needed for the SPI path. Doesn't the I2C
> subsystem overwrite the rx buffer with what it reads from the device?

I thought it's best practice to ensure that old conversions are not accidentally re-used in case the read operation fell thru the cracks.
that's exactly why in this particular case the BUSY flag is implemented on the hardware side.

please tell me how a few byte memset() would be detrimental.

best regards,
peter

> >  	ret = data->ops->read(data, MPR_CMD_NOP, MPR_PKT_NOP_LEN);
> >  	if (ret < 0)
> >  		return ret;
> > diff --git a/drivers/iio/pressure/mprls0025pa_i2c.c b/drivers/iio/pressure/mprls0025pa_i2c.c
> > index a0bbc6af9283..0fe8cfe0d7e7 100644
> > --- a/drivers/iio/pressure/mprls0025pa_i2c.c
> > +++ b/drivers/iio/pressure/mprls0025pa_i2c.c
> > @@ -25,7 +25,6 @@ static int mpr_i2c_read(struct mpr_data *data, const u8 unused, const u8 cnt)
> >  	if (cnt > MPR_MEASUREMENT_RD_SIZE)
> >  		return -EOVERFLOW;
> >  
> > -	memset(data->rx_buf, 0, MPR_MEASUREMENT_RD_SIZE);
> >  	ret = i2c_master_recv(client, data->rx_buf, cnt);
> >  	if (ret < 0)
> >  		return ret;

-- 
petre rodan

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