linux-kernel - Re: [PATCH v3 0/6] iio: Add output buffer support

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Message-ID: <20210308115203.00006230@Huawei.com>
Date:   Mon, 8 Mar 2021 11:52:03 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     "Sa, Nuno" <Nuno.Sa@...log.com>,
        Jonathan Cameron <jic23@...nel.org>
CC:     "Hennerich, Michael" <Michael.Hennerich@...log.com>,
        "zzzzArdelean, zzzzAlexandru" <alexandru.Ardelean@...log.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "lars@...afoo.de" <lars@...afoo.de>,
        "Bogdan, Dragos" <Dragos.Bogdan@...log.com>
Subject: Re: [PATCH v3 0/6] iio: Add output buffer support

On Mon, 8 Mar 2021 10:07:05 +0000
"Sa, Nuno" <Nuno.Sa@...log.com> wrote:

> > -----Original Message-----
> > From: Jonathan Cameron <jic23@...nel.org>
> > Sent: Saturday, March 6, 2021 6:35 PM
> > To: Hennerich, Michael <Michael.Hennerich@...log.com>
> > Cc: zzzzArdelean, zzzzAlexandru <alexandru.Ardelean@...log.com>;
> > linux-kernel@...r.kernel.org; linux-iio@...r.kernel.org;
> > lars@...afoo.de; Sa, Nuno <Nuno.Sa@...log.com>; Bogdan, Dragos
> > <Dragos.Bogdan@...log.com>
> > Subject: Re: [PATCH v3 0/6] iio: Add output buffer support
> > 
> > On Fri, 5 Mar 2021 08:57:08 +0000
> > "Hennerich, Michael" <Michael.Hennerich@...log.com> wrote:
> >   
> > > Hi Jonathan and others,
> > >
> > > With output/dac buffer support the semantics of the scan_element  
> > type may change.  
> > >
> > > Today the Format is [be|le]:[s|u]bits/storagebitsXrepeat[>>shift].
> > >
> > > While shift (if specified) is the shift that needs to be applied prior to  
> > masking out unused bits.  
> > >
> > > So far so good and it sounds universal.
> > >
> > > However, we use the right shift (operator) for that, which makes  
> > sense for capture devices.  
> > > For output devices the more logical operator would be the left shift.
> > >
> > > I'm not proposing a new Format here. I just want to get some  
> > agreement that for an output device  
> > >  
> > > le:s12/16>>4  
> > >
> > > is understood as a left shift of 4, since the unused bits are then on  
> > the LSB.
> > 
> > Good question. Guess I wasn't thinking ahead when I came up with
> > that :)
> > 
> > I'm not sure I'd mind if we did decide to define a new format for
> > output
> > buffers. Feels like it should be easy to do.
> > 
> > What do others think?
> >   
> 
> I guess the most straight forward thing would be just to add a 'shift_l' variable
> to 'struct scan_type'' and make sure either 'shift_l' or 'shift' is defined and then
> properly export either ">>" or "<<" to userspace?

Given we already know it's an output channel, can we not just use that
to make the decision?

Jonathan

> 
> - Nuno Sá 
>