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

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Message-ID: <CY4PR03MB26318300B44C07A5890067B499939@CY4PR03MB2631.namprd03.prod.outlook.com>
Date:   Mon, 8 Mar 2021 10:07:05 +0000
From:   "Sa, Nuno" <Nuno.Sa@...log.com>
To:     Jonathan Cameron <jic23@...nel.org>,
        "Hennerich, Michael" <Michael.Hennerich@...log.com>
CC:     "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


> -----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?

- Nuno Sá