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Date:   Mon, 30 Aug 2021 15:29:56 +0100
From:   Jonathan Cameron <jic23@kernel.org>
To:     "Sa, Nuno" <Nuno.Sa@analog.com>
Cc:     Miquel Raynal <miquel.raynal@bootlin.com>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        "linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 03/16] iio: adc: max1027: Push only the requested
 samples
Message-ID: <20210830152956.58331a8d@jic23-huawei>
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        <20210830110756.733d5201@jic23-huawei>
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On Mon, 30 Aug 2021 10:49:50 +0000
"Sa, Nuno" <Nuno.Sa@analog.com> wrote:

> > -----Original Message-----
> > From: Jonathan Cameron <jic23@kernel.org>
> > Sent: Monday, August 30, 2021 12:08 PM
> > To: Sa, Nuno <Nuno.Sa@analog.com>
> > Cc: Miquel Raynal <miquel.raynal@bootlin.com>; Lars-Peter Clausen
> > <lars@metafoo.de>; Thomas Petazzoni
> > <thomas.petazzoni@bootlin.com>; linux-iio@vger.kernel.org; linux-
> > kernel@vger.kernel.org
> > Subject: Re: [PATCH 03/16] iio: adc: max1027: Push only the requested
> > samples
> > 
> > [External]
> > 
> > On Fri, 20 Aug 2021 07:10:48 +0000
> > "Sa, Nuno" <Nuno.Sa@analog.com> wrote:
> >   
> > > > -----Original Message-----
> > > > From: Miquel Raynal <miquel.raynal@bootlin.com>
> > > > Sent: Wednesday, August 18, 2021 1:11 PM
> > > > To: Jonathan Cameron <jic23@kernel.org>; Lars-Peter Clausen
> > > > <lars@metafoo.de>
> > > > Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>; linux-
> > > > iio@vger.kernel.org; linux-kernel@vger.kernel.org; Miquel Raynal
> > > > <miquel.raynal@bootlin.com>
> > > > Subject: [PATCH 03/16] iio: adc: max1027: Push only the requested
> > > > samples
> > > >
> > > > [External]
> > > >
> > > > When a triggered scan occurs, the identity of the desired channels  
> > is  
> > > > known in indio_dev->active_scan_mask. Instead of reading and
> > > > pushing to
> > > > the IIO buffers all channels each time, scan the minimum amount  
> > of  
> > > > channels (0 to maximum requested chan, to be exact) and only
> > > > provide the
> > > > samples requested by the user.
> > > >
> > > > For example, if the user wants channels 1, 4 and 5, all channels  
> > from  
> > > > 0 to 5 will be scanned but only the desired channels will be pushed  
> > to  
> > > > the IIO buffers.
> > > >
> > > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > > > ---
> > > >  drivers/iio/adc/max1027.c | 25 +++++++++++++++++++++----
> > > >  1 file changed, 21 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/drivers/iio/adc/max1027.c b/drivers/iio/adc/max1027.c
> > > > index b753658bb41e..8ab660f596b5 100644
> > > > --- a/drivers/iio/adc/max1027.c
> > > > +++ b/drivers/iio/adc/max1027.c
> > > > @@ -360,6 +360,9 @@ static int max1027_set_trigger_state(struct
> > > > iio_trigger *trig, bool state)
> > > >  	struct max1027_state *st = iio_priv(indio_dev);
> > > >  	int ret;
> > > >
> > > > +	if (bitmap_empty(indio_dev->active_scan_mask, indio_dev-  
> > > > >masklength))  
> > > > +		return -EINVAL;
> > > > +  
> > >
> > > I'm not sure this can actually happen. If you try to enable the buffer
> > > with no scan element, it should give you an error before you reach
> > > this point...
> > >  
> > > >  	if (state) {
> > > >  		/* Start acquisition on cnvst */
> > > >  		st->reg = MAX1027_SETUP_REG |
> > > > MAX1027_CKS_MODE0 |
> > > > @@ -368,9 +371,12 @@ static int max1027_set_trigger_state(struct
> > > > iio_trigger *trig, bool state)
> > > >  		if (ret < 0)
> > > >  			return ret;
> > > >
> > > > -		/* Scan from 0 to max */
> > > > -		st->reg = MAX1027_CONV_REG | MAX1027_CHAN(0) |
> > > > -			  MAX1027_SCAN_N_M | MAX1027_TEMP;
> > > > +		/*
> > > > +		 * Scan from 0 to the highest requested channel. The
> > > > temperature
> > > > +		 * could be avoided but it simplifies a bit the logic.
> > > > +		 */
> > > > +		st->reg = MAX1027_CONV_REG |
> > > > MAX1027_SCAN_0_N | MAX1027_TEMP;
> > > > +		st->reg |= MAX1027_CHAN(fls(*indio_dev-  
> > > > >active_scan_mask) - 2);  
> > > >  		ret = spi_write(st->spi, &st->reg, 1);
> > > >  		if (ret < 0)
> > > >  			return ret;
> > > > @@ -391,11 +397,22 @@ static irqreturn_t
> > > > max1027_trigger_handler(int irq, void *private)
> > > >  	struct iio_poll_func *pf = private;
> > > >  	struct iio_dev *indio_dev = pf->indio_dev;
> > > >  	struct max1027_state *st = iio_priv(indio_dev);
> > > > +	unsigned int scanned_chans = fls(*indio_dev-  
> > > > >active_scan_mask);  
> > > > +	u16 *buf = st->buffer;  
> > >
> > > I think sparse will complain here. buffer is a __be16 restricted
> > > type so you should not mix those...  
> > > > +	unsigned int bit;
> > > >
> > > >  	pr_debug("%s(irq=%d, private=0x%p)\n", __func__, irq,
> > > >  
> > private);in/20210818_miquel_raynal_bring_software_triggers_support
> > _to_max1027_like_adcs.mbx  
> > > >
> > > >  	/* fill buffer with all channel */
> > > > -	spi_read(st->spi, st->buffer, indio_dev->masklength * 2);
> > > > +	spi_read(st->spi, st->buffer, scanned_chans * 2);
> > > > +
> > > > +	/* Only keep the channels selected by the user */
> > > > +	for_each_set_bit(bit, indio_dev->active_scan_mask,
> > > > +			 indio_dev->masklength) {
> > > > +		if (buf[0] != st->buffer[bit])
> > > > +			buf[0] = st->buffer[bit];  
> > >
> > > Since we are here, when looking into the driver, I realized
> > > that st->buffer is not DMA safe. In IIO, we kind of want to enforce
> > > that all buffers that are passed to spi/i2c buses are safe... Maybe
> > > this is something you can include in your series.  
> > 
> > Why is it not?  st->buffer is result of a devm_kmalloc_array() call and
> > that should provide a DMA safe buffer as I understand it.
> >   
> 
> That's a good question. I'm not sure how I came to that conclusion which
> is clearly wrong. Though I think the buffer might share the line with the
> mutex...
Pointer shares a line.  The buffer it points to doesn't as allocated
by separate heap allocation.

J
> 
> - Nuno Sá
>