linux-kernel - Re: Multiplex SPI Chip Selects

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Date:   Mon, 6 Jan 2020 22:51:38 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>
Cc:     "dries.vanpuymbroeck@...imo.com" <dries.vanpuymbroeck@...imo.com>,
        "anthony.derosa@...call7.com" <anthony.derosa@...call7.com>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Multiplex SPI Chip Selects

On Mon, Jan 06, 2020 at 10:44:15PM +0000, Chris Packham wrote:
> On Mon, 2020-01-06 at 08:27 -0500, Anthony DeRosa wrote:

As documented in submitting-patches.rst please send patches to the 
maintainers for the code you would like to change.  The normal kernel
workflow is that people apply patches from their inboxes, if they aren't
copied they are likely to not see the patch at all and it is much more
difficult to apply patches.

> > This proposed patch does exactly what I need to do:
> > https://patchwork.kernel.org/patch/2706151/, but I was wondering why
> > nothing like this already exists or why that patch had not been
> > included in the mainline kernel.

> I don't know why Dries' patch series didn't land. The reason my one
> didn't land was due to some implementation details and the ability to
> do something simpler with a fake gpio.

If you want me to review something you'l need to submit it; that patch
was from 2013 so predates me maintaining the subsystem so I've never
seen a copy.

My general instinct with this stuff is that it's likely to be more
sensible to describe this with GPIO chip selects, the state of
controller chip selects is such that a lot of devices use them anyway
even when the controller supports native chip selects as the controller
chip selects often suffer from unfortunate limitations that mean they're
not actually useful.

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