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Subject: Re: [Letux-kernel] [BUG] SPI broken for SPI based panel drivers
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From:   "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <20201201174433.2000c8a3@aktux>
Date:   Tue, 1 Dec 2020 17:52:34 +0100
Cc:     Sven Van Asbroeck <thesven73@gmail.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@openphoenux.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Mark Brown <broonie@kernel.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>
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References: <2D7916FA-678F-4236-B478-C953CADF2FFA@goldelico.com> <CAGngYiXgc_m2A7Wihxuhzm-u4qH-JZgxHjke653zvyT45jMU7Q@mail.gmail.com> <4AC29229-9542-4E77-B993-217E29C7E209@goldelico.com> <20201201121620.GB5239@sirena.org.uk> <A499CCB9-F2EC-4F24-AA79-5A7FA6A092A9@goldelico.com> <CACRpkdYf2dUF6PjYcvnsKDPoxXPWiWKKAqpik4-2AAQjRmatfw@mail.gmail.com> <6283C16F-549C-4463-BC08-E2C1A1D78B2F@goldelico.com> <CAGngYiUG76Q-cb_HdDKMia5yXzv_mS+5NPeaBquK3_4b3tr-4Q@mail.gmail.com> <20201201174433.2000c8a3@aktux>
To:     Andreas Kemnade <andreas@kemnade.info>
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> Am 01.12.2020 um 17:44 schrieb Andreas Kemnade <andreas@kemnade.info>:
>=20
> On Tue, 1 Dec 2020 11:10:49 -0500
> Sven Van Asbroeck <thesven73@gmail.com> wrote:
>=20
>> Nikolaus,
>>=20
>> On Tue, Dec 1, 2020 at 9:38 AM H. Nikolaus Schaller =
<hns@goldelico.com> wrote:
>>>=20
>>> Let's work on a fix for the fix now.
>>>=20
>>=20
>> 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?
>>=20
> Schematics is here:
> https://projects.goldelico.com/p/gta04-main/downloads/48/
>=20
> The display connector P204-LCD indicates some inversion at the XCS and
> XRES pins.
>=20
> 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 =3D <100000>;
>                        spi-cpol;
>                        spi-cpha;
> -                       spi-cs-high;

BTW: that is what I had planned to try next...

>=20
>                        backlight=3D <&backlight>;
>                        label =3D "lcd";
>=20
> So if that one is really active-low, why did it ever work?!
>=20
> Regards,
> Andreas