linux-kernel - Re: [PATCH v2 3/6] spi: dw: Add Microchip Sparx5 support

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Message-ID: <20200623140815.GF5582@sirena.org.uk>
Date:   Tue, 23 Jun 2020 15:08:15 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Lars Povlsen <lars.povlsen@...rochip.com>
Cc:     Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Serge Semin <fancer.lancer@...il.com>,
        Serge Semin <Sergey.Semin@...kalelectronics.ru>
Subject: Re: [PATCH v2 3/6] spi: dw: Add Microchip Sparx5 support

On Tue, Jun 23, 2020 at 03:53:22PM +0200, Lars Povlsen wrote:
> Mark Brown writes:

> >If there's a mux that needs to be handled specially that mux should be
> >described in DT on the relevant boards, there shouldn't just be
> >something hard coded in the controller driver.

> I looked at the spi-mux driver, but that is more for muxing the CS's, as
> I understand - not the actual bus segment. I could use it, but it would

It doesn't matter that much exactly what signals get switched I think,
we can't really tell by the time we get back to the controller.

> require encoding the bus segment into the CS (double the normal
> range). Also, selecting the bus interface is tightly coupled to the
> controller - its not an externally constructed board mux.

It sounds like this controller should be describing a mux all the time -
if there's completely separate output buses that you can switch between
then we'll need to know about that if someone wires up a GPIO chip
select.

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