linux-kernel - Re: [BUG] gpiolib: spi chip select legacy support breaks modern chip select and whitens the GTA04 LCD panel

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Message-ID: <20190402091659.GD2059@sirena.org.uk>
Date:   Tue, 2 Apr 2019 16:16:59 +0700
From:   Mark Brown <broonie@...nel.org>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Kumar Gala <galak@...eaurora.org>,
        Wolfgang Ocker <weo@...coware.de>,
        Jan Kotas <jank@...ence.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>, kernel@...a-handheld.com,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [BUG] gpiolib: spi chip select legacy support breaks modern chip
 select and whitens the GTA04 LCD panel

On Tue, Apr 02, 2019 at 08:37:23AM +0200, H. Nikolaus Schaller wrote:

> I have learned from Linus that the problem with legacy spi-cs-high are mostly embedded
> powerpc systems deployed between 2008 and 2013 where the boot-loader can't be
> changed. And where the dts is not maintained on kernel.org.

> IMHO it is very unlikely that they are running distro kernels. Or is there an example
> of such a system?

I used to work on embedded systems which were built by essentially
bolting expansion cards onto standard reference systems, for some of
them we shipped distro kernels with the extra hardware supported by
adding modules.  No idea if there's practical examples for specific
PowerPC systems though.

The burden when you're breaking things is more on showing that there
isn't a problem anyway...

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