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Message-ID: <61147de8e3761c5d3c000ee5ea0d9d146da89602.camel@gmail.com>
Subject: Re: [PATCH RFC v2 1/8] spi: dt-bindings: spi-peripheral-props: add
 spi-offloads property
From: Nuno =?ISO-8859-1?Q?S=E1?= <noname.nuno@gmail.com>
To: David Lechner <dlechner@baylibre.com>, Conor Dooley <conor@kernel.org>
Cc: Mark Brown <broonie@kernel.org>, Jonathan Cameron <jic23@kernel.org>, 
 Rob Herring <robh@kernel.org>, Krzysztof Kozlowski <krzk+dt@kernel.org>,
 Conor Dooley <conor+dt@kernel.org>,  Nuno =?ISO-8859-1?Q?S=E1?=
 <nuno.sa@analog.com>, Michael Hennerich <Michael.Hennerich@analog.com>, 
 Lars-Peter Clausen <lars@metafoo.de>, David Jander <david@protonic.nl>,
 Martin Sperl <kernel@martin.sperl.org>, linux-spi@vger.kernel.org, 
 devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, 
 linux-iio@vger.kernel.org
Date: Thu, 23 May 2024 17:30:45 +0200
In-Reply-To: <3fad2e61-c3e4-4bb1-bbea-101d5d0f91ee@baylibre.com>
References: 
	<20240510-dlech-mainline-spi-engine-offload-2-v2-0-8707a870c435@baylibre.com>
	 <20240510-dlech-mainline-spi-engine-offload-2-v2-1-8707a870c435@baylibre.com>
	 <20240513-headsman-hacking-d51fcc811695@spud>
	 <CAMknhBE5XJzhdJ=PQUXiubw_CiCLcn1jihiscnQZUzDWMASPKw@mail.gmail.com>
	 <20240514-aspire-ascension-449556da3615@spud>
	 <CAMknhBFFpEGcMoLo5gsC11Syv+CwUM0mnq1yDMUzL1uutUtB+Q@mail.gmail.com>
	 <20240516-rudder-reburial-dcf300504c0a@spud>
	 <CAMknhBF_s0btus4yqPe-T=F3z7Asi9KkRGsGr7FHDFi=k4EQjw@mail.gmail.com>
	 <20240519-abreast-haziness-096a57ef57d3@spud>
	 <CAMknhBHvEse2FyDoBXR1PvymGpSGq8dotKfm+8XH+0+k+xKtQw@mail.gmail.com>
	 <20240522-gullible-ibuprofen-cf9111c25f6f@spud>
	 <59df2cc3-5a62-45be-a0aa-5bbff13c2ae4@baylibre.com>
	 <35de37c08331a8384aa9ebde3a9be5fec6fc418e.camel@gmail.com>
	 <3fad2e61-c3e4-4bb1-bbea-101d5d0f91ee@baylibre.com>
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On Thu, 2024-05-23 at 10:09 -0500, David Lechner wrote:
> On 5/23/24 9:57 AM, Nuno S=C3=A1 wrote:
> > On Thu, 2024-05-23 at 09:28 -0500, David Lechner wrote:
> > > On 5/22/24 1:24 PM, Conor Dooley wrote:
> > > > On Tue, May 21, 2024 at 09:54:39AM -0500, David Lechner wrote:
> > > > > On Sun, May 19, 2024 at 7:53=E2=80=AFAM Conor Dooley <conor@kerne=
l.org> wrote:
> > > > > >=20
> > > > > > On Fri, May 17, 2024 at 11:51:58AM -0500, David Lechner wrote:
> > > > > > > On Thu, May 16, 2024 at 4:32=E2=80=AFPM Conor Dooley <conor@k=
ernel.org> wrote:
> > > > > > > > On Tue, May 14, 2024 at 05:56:47PM -0500, David Lechner wro=
te:
> > > > > >=20
> > >=20
> >=20
> > ...
> >=20
> > >=20
> > > controller:
> > > #spi-offload-cells =3D <2>: /* 1st cell =3D offload instance
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0 * 2nd cell =3D trigger provider */
> > >=20
> >=20
> > What about things like DMA? I'm mentioning it a lot because it's way mo=
re complex
> > having it on the controller (from a SW perspective). But from an HW poi=
nt of
> > view,
> > it's always very similar (if not the same) as your case A.
> >=20
>=20
> If we had a setup where there was more than one place that, e.g. the
> RX stream from the offload could be piped, then I would add a 3rd
> cell to describe that. If the hardware is fixed and the RX stream
> always goes to a specific DMA channel, then it doesn't seem like we
> need to describe that in the SPI controller node because the hardware
> is fixed.
>=20

Well, yes, still the DMA channel is connected on the controller and not the
peripheral. Same deal as we discussed on the IIO backends stuff. But there,=
 since
it's all IIO it was easy to make the DMA a property of the backend device. =
That said,
I can surely see having the property in the peripheral.

Another thing that came to mind for the trigger case. What about an additio=
nal spi
interface for configuring/setting the trigger rate? Sounds generic and then=
 we would
not really need the trigger on the peripheral right (did not checked the CR=
C issue
you mentioned so not sure if it's somehow trigger related)?

Hmm but sometimes there's other things than rate/period (like offset) to ca=
re about
so maybe not doable... Bah!

- Nuno S=C3=A1