Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   "Sa, Nuno" <Nuno.Sa@analog.com>
To:     Jonathan Cameron <Jonathan.Cameron@Huawei.com>,
        Jonathan Cameron <jic23@kernel.org>
CC:     "Hennerich, Michael" <Michael.Hennerich@analog.com>,
        "zzzzArdelean, zzzzAlexandru" <alexandru.Ardelean@analog.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>,
        "lars@metafoo.de" <lars@metafoo.de>,
        "Bogdan, Dragos" <Dragos.Bogdan@analog.com>
Subject: RE: [PATCH v3 0/6] iio: Add output buffer support
Thread-Topic: [PATCH v3 0/6] iio: Add output buffer support
Thread-Index: AQHXBrxjq9QBbWMRtka/kQD4wV/AUapihP4AgBKolACAAiL4gIACpXPggAAfcoCAABE7cA==
Date:   Mon, 8 Mar 2021 13:00:37 +0000
Message-ID: <CY4PR03MB26318FE58CDB5301224EAC9399939@CY4PR03MB2631.namprd03.prod.outlook.com>
References: <20210219124012.92897-1-alexandru.ardelean@analog.com>
        <20210221120106.00ae1078@archlinux>
        <BN8PR03MB497724AAAFA43E6555554DC98E969@BN8PR03MB4977.namprd03.prod.outlook.com>
        <20210306173449.06f2f32b@archlinux>
        <CY4PR03MB26318300B44C07A5890067B499939@CY4PR03MB2631.namprd03.prod.outlook.com>
 <20210308115203.00006230@Huawei.com>
In-Reply-To: <20210308115203.00006230@Huawei.com>
Accept-Language: en-US
Content-Language: en-US
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: aaf42b1f-5413-4553-37a8-08d8e2322ba4
X-MS-Exchange-CrossTenant-originalarrivaltime: 08 Mar 2021 13:00:37.9260
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: eaa689b4-8f87-40e0-9c6f-7228de4d754a
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: Utbkr2TXxlK7DVupswDfWxWjWdugi/Tbnamxp4oLgtnPElEkHrvW508zqFX5AJRLZq7tiVSoWoTFIX+nglEUFg==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR03MB2869
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.369,18.0.761
 definitions=2021-03-08_08:2021-03-08,2021-03-08 signatures=0
X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 adultscore=0
 lowpriorityscore=0 spamscore=0 mlxlogscore=999 priorityscore=1501
 malwarescore=0 bulkscore=0 phishscore=0 suspectscore=0 mlxscore=0
 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1
 engine=8.12.0-2009150000 definitions=main-2103080067
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


> -----Original Message-----
> From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
> Sent: Monday, March 8, 2021 12:52 PM
> To: Sa, Nuno <Nuno.Sa@analog.com>; Jonathan Cameron
> <jic23@kernel.org>
> Cc: Hennerich, Michael <Michael.Hennerich@analog.com>;
> zzzzArdelean, zzzzAlexandru <alexandru.Ardelean@analog.com>;
> linux-kernel@vger.kernel.org; linux-iio@vger.kernel.org;
> lars@metafoo.de; Bogdan, Dragos <Dragos.Bogdan@analog.com>
> Subject: Re: [PATCH v3 0/6] iio: Add output buffer support
>=20
> [External]
>=20
> On Mon, 8 Mar 2021 10:07:05 +0000
> "Sa, Nuno" <Nuno.Sa@analog.com> wrote:
>=20
> > > -----Original Message-----
> > > From: Jonathan Cameron <jic23@kernel.org>
> > > Sent: Saturday, March 6, 2021 6:35 PM
> > > To: Hennerich, Michael <Michael.Hennerich@analog.com>
> > > Cc: zzzzArdelean, zzzzAlexandru
> <alexandru.Ardelean@analog.com>;
> > > linux-kernel@vger.kernel.org; linux-iio@vger.kernel.org;
> > > lars@metafoo.de; Sa, Nuno <Nuno.Sa@analog.com>; Bogdan,
> Dragos
> > > <Dragos.Bogdan@analog.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@analog.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 pr=
ior
> 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 def=
ined
> and then
> > properly export either ">>" or "<<" to userspace?
>=20
> Given we already know it's an output channel, can we not just use that
> to make the decision?
>=20
> Jonathan

I would argue that having two variables gives us more flexibility for whate=
ver
the future brings us :). But if we can sanely say that an output buffer wil=
l
always use left shifts, then we could definitely use that information... I =
mean,
we are already doing that assumption for input buffers and right shifts...

- Nuno S=E1