linux-kernel - Re: [PATCH 3/6] spi: add multi_bus_mode field to struct spi

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Message-ID: <9024f05854dcc3cc59345c0a3de900f57c4730d9.camel@gmail.com>
Date: Wed, 15 Oct 2025 17:43:22 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: David Lechner <dlechner@...libre.com>, Mark Brown <broonie@...nel.org>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
  Conor Dooley <conor+dt@...nel.org>, Marcelo Schmitt
 <marcelo.schmitt@...log.com>, Michael Hennerich	
 <michael.hennerich@...log.com>, Nuno Sá
 <nuno.sa@...log.com>,  Jonathan Cameron	 <jic23@...nel.org>, Andy
 Shevchenko <andy@...nel.org>, Sean Anderson	 <sean.anderson@...ux.dev>,
 linux-spi@...r.kernel.org, 	devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, 	linux-iio@...r.kernel.org
Subject: Re: [PATCH 3/6] spi: add multi_bus_mode field to struct spi_transfer

On Wed, 2025-10-15 at 11:15 -0500, David Lechner wrote:
> On 10/15/25 10:18 AM, Mark Brown wrote:
> > On Wed, Oct 15, 2025 at 03:43:09PM +0100, Nuno Sá wrote:
> > > On Wed, 2025-10-15 at 13:01 +0100, Mark Brown wrote:
> > > > On Wed, Oct 15, 2025 at 11:16:01AM +0100, Nuno Sá wrote:
> > > > > On Tue, 2025-10-14 at 17:02 -0500, David Lechner wrote:
> > 
> > > > > >         controller    < data bits <     peripheral
> > > > > >         ----------   ----------------   ----------
> > > > > >             SDI 0    0-0-0-1-0-0-0-1    SDO 0
> > > > > >             SDI 1    1-0-0-0-1-0-0-0    SDO 1
> > 
> > > > > Out of curiosity, how does this work for devices like AD4030 where the same
> > > > > word
> 
> The AD4030 is just one channel, so doesn't do interleaving. But you probably
> meant AD4630 when it is wired up with only 1 SDO line. That line has to be shared
> by both of the simultaneous converters so it alternates between sending one bit
> from each word. This patch series doesn't address that case. But this series will
> work for the AD4630 when it has 2 SDO lines wired up.
> 

Hmm I didn't even remembered that one. But what I meant with interleaved was having
the same data word spread through multiple SDO lines (one bit per line) which is what
(also) happens with the devices I mentioned. And since you mentioned "...two
different data words at the same time, one on each bus...", I raised the question.

So I guess I kind of misused what interleaved typically means (even though I guess
it's not completely off :)) and was thinking more on the parallel concept Mark spoke
about.

Anyways, from your reply I see the intent is to also use the stripe mode for this and
have some kind of external IP deal with data re-order. I gave a look into the ad4630
IP core and indeed there's a data reorder IP block after the offload engine.

- Nuno Sá

> > > >