linux-kernel - Re: [PATCH 01/13] spi: add core support for controllers with offload capabilities

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Date: Thu, 11 Jan 2024 15:41:09 +0000
From: Mark Brown <broonie@...nel.org>
To: Nuno Sá <noname.nuno@...il.com>
Cc: David Lechner <dlechner@...libre.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Michael Hennerich <michael.hennerich@...log.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Frank Rowand <frowand.list@...il.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
	Jonathan Corbet <corbet@....net>, linux-spi@...r.kernel.org,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-pwm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/13] spi: add core support for controllers with offload
 capabilities

On Thu, Jan 11, 2024 at 03:11:32PM +0100, Nuno Sá wrote:
> On Thu, 2024-01-11 at 13:33 +0000, Mark Brown wrote:

> > I tend to agree that we shouldn't be exposing this to SPI device drivers
> > however we will want to keep track of if the unit is busy, and designing
> > it to cope with multiple offloads does seem like sensible future
> > proofing.  There's also the possibility that one engine might be able to

> Fair enough. But wouldn't a simple DT integer property (handled by the spi core)
> to identify the offload index be easier for SPI device drivers? We could still
> have dedicated interfaces for checking if the unit is busy or not... The point
> is that we would not need an explicit get() from SPI drivers.

It feels like we'd need a get/release operation of some kind for mutual
exclusion, it's not just the discovery it's also figuring out if the
hardware is in use at a given moment.

> I'm of course assuming that one spi device can only be connected to one engine
> which seems reasonable to me.

I can see someone implementing this with for example the microcontroller
cores a lot of SoCs have in which case all bets are off.

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