linux-kernel - Re: (EXT) Re: (EXT) Re: [PATCH] spi-imx: remove num-cs support, set num

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Message-ID: <f753882996235439b9ef53747d24382e896dc4e7.camel@ew.tq-group.com>
Date:   Fri, 04 Sep 2020 16:34:43 +0200
From:   Matthias Schiffer <matthias.schiffer@...tq-group.com>
To:     Fabio Estevam <festevam@...il.com>
Cc:     Mark Brown <broonie@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        linux-spi <linux-spi@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: (EXT) Re: (EXT) Re: [PATCH] spi-imx: remove num-cs support, set
 num_chipselect to 4

On Fri, 2020-09-04 at 10:57 -0300, Fabio Estevam wrote:
> On Fri, Sep 4, 2020 at 10:02 AM Matthias Schiffer
> <matthias.schiffer@...tq-group.com> wrote:
> 
> > This would make num_chipselect default to 1 again (set by
> > __spi_alloc_controller()), breaking every i.MX board that uses more
> > than 1 native CS.
> 
> Which boards are that? Are you referring to non-DT i.MX boards?
> 
> If so, I have sent a patch removing all non-DT i.MX boards.
> 
> > I'm aware that using cs-gpios instead of native CS is probably a
> > good
> > idea in any case, as the native CS of this SPI controller is kinda
> > flaky (and at a glance it looks like all in-tree DTs do this; not
> > sure
> > about board files that don't use DTs?), but I'm not convinced that
> > breaking native CS support completely is desirable either.
> 
> Initial i.MX chips with this SPI IP had issues in using chip-select
> in
> native mode and GPIO chip-select has been used since them.
> 
> Do we have i.MX dts that make use of native chip select?

As mentioned in my previous mail, all in-tree DTS use cs-gpios (unless
I've overlooked something - I grepped for CSPIn_SSm pinmuxings), so
removing support for native CS should not break anything we know of.

Nevertheless, I don't see why we should deliberately remove the native
CS support - my understanding was that we try to avoid breaking changes
to DT interpretation even for unknown/out-of-tree DTS.