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

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Date:   Tue, 1 Dec 2020 17:51:12 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Andreas Kemnade <andreas@...nade.info>
Cc:     Sven Van Asbroeck <thesven73@...il.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>,
        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


> Am 01.12.2020 um 17:44 schrieb Andreas Kemnade <andreas@...nade.info>:
> 
> 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?!

Apparently, because there was patch f1f028ff89cb0d3 to fix 6953c57ab172 ...

BR,
Nikolaus