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Date: Thu, 11 Jan 2024 21:49:53 +0000
From: Mark Brown <broonie@kernel.org>
To: David Lechner <dlechner@baylibre.com>
Cc: Jonathan Cameron <jic23@kernel.org>, Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Michael Hennerich <michael.hennerich@analog.com>,
	Nuno =?iso-8859-1?Q?S=E1?= <nuno.sa@analog.com>,
	Frank Rowand <frowand.list@gmail.com>,
	Thierry Reding <thierry.reding@gmail.com>,
	Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= <u.kleine-koenig@pengutronix.de>,
	Jonathan Corbet <corbet@lwn.net>, linux-spi@vger.kernel.org,
	linux-iio@vger.kernel.org, devicetree@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-pwm@vger.kernel.org,
	linux-kernel@vger.kernel.org, David Jander <david@protonic.nl>
Subject: Re: [PATCH 01/13] spi: add core support for controllers with offload
 capabilities
Message-ID: <829ac770-1955-45b7-9033-6ed60ffdf77e@sirena.org.uk>
References: <20240109-axi-spi-engine-series-3-v1-0-e42c6a986580@baylibre.com>
 <20240109-axi-spi-engine-series-3-v1-1-e42c6a986580@baylibre.com>
 <2c74aad9-3cb9-4222-8072-e72120c2658e@sirena.org.uk>
 <CAMknhBGMRed9vDrDAuPJ5DnEe6MyHzd0VBebp5OaLX2Q+AyhMQ@mail.gmail.com>
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On Thu, Jan 11, 2024 at 03:32:54PM -0600, David Lechner wrote:
> On Thu, Jan 11, 2024 at 2:54=E2=80=AFPM David Lechner <dlechner@baylibre.=
com> wrote:

> > > (CCed) a while back when he was doing all the work he did on optimisi=
ng
> > > the core for uncontended uses, the thinking there was to have a
> > > spi_prepare_message() (or similar) API that drivers could call and th=
en
> > > reuse the same transfer repeatedly, and even without any interface for
> > > client drivers it's likely that we'd be able to take advantage of it =
in
> > > the core for multi-transfer messages.  I'd be surprised if there were=
n't
> > > wins when the message goes over the DMA copybreak size.  A much wider
> > > range of hardware would be able to do this bit, for example David's c=
ase
> > > was a Raspberry Pi using the DMA controller to write into the SPI

> For those, following along, it looks like the RPi business was
> actually a 2013 discussion with Martin Sperl [2]. Both this and [1]
> discuss proposed spi_prepare_message() APIs.

> [2]: https://lore.kernel.org/linux-spi/CACRpkdb4mn_Hxg=3D3tuBu89n6eyJ082E=
ETkwtNbzZDFZYTHbVVg@mail.gmail.com/T/#u

Oh, yes - sorry, I'd misremembered which optimisation effort it was
associated with.  Apologies.

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