linux-kernel - Re: [Letux-kernel] [BUG] SPI broken for SPI based panel drivers

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Date:   Tue, 1 Dec 2020 17:44:33 +0100
From:   Andreas Kemnade <andreas@...nade.info>
To:     Sven Van Asbroeck <thesven73@...il.com>
Cc:     Discussions about the Letux Kernel <letux-kernel@...nphoenux.org>,
        "H. Nikolaus Schaller" <hns@...delico.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [Letux-kernel] [BUG] SPI broken for SPI based panel drivers

On Tue, 1 Dec 2020 11:10:49 -0500
Sven Van Asbroeck <thesven73@...il.com> wrote:

> Nikolaus,
> 
> On Tue, Dec 1, 2020 at 9:38 AM H. Nikolaus Schaller <hns@...delico.com> wrote:
> >
> > Let's work on a fix for the fix now.
> >  
> 
> Are you quite sure the chip-select of the tpo,td028ttec1 panel
> is active-high? A quick google produced a datasheet which
> seems to indicate that XCS is active-low?
> 
Schematics is here:
https://projects.goldelico.com/p/gta04-main/downloads/48/

The display connector P204-LCD indicates some inversion at the XCS and
XRES pins.

This patch fixes things for a boot where the display was not
touched by the bootloader
diff --git a/arch/arm/boot/dts/omap3-gta04.dtsi b/arch/arm/boot/dts/omap3-gta04.dtsi
index c8745bc800f7..003202d12990 100644
--- a/arch/arm/boot/dts/omap3-gta04.dtsi
+++ b/arch/arm/boot/dts/omap3-gta04.dtsi
@@ -124,7 +124,6 @@
                        spi-max-frequency = <100000>;
                        spi-cpol;
                        spi-cpha;
-                       spi-cs-high;
 
                        backlight= <&backlight>;
                        label = "lcd";

So if that one is really active-low, why did it ever work?!

Regards,
Andreas