linux-kernel - Re: [PATCH 0/6] drm/sun4i: Support color dithering for LCD panels

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Message-ID: <CAMty3ZAPGuxLB99jod8Mq1fF+Mw6GLpLHiGuSHRNFKOT2uJSOQ@mail.gmail.com>
Date:   Wed, 5 Sep 2018 18:54:29 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Maxime Ripard <maxime.ripard@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Jonathan Liu <net147@...il.com>
Subject: Re: [PATCH 0/6] drm/sun4i: Support color dithering for LCD panels

On Thu, Apr 19, 2018 at 3:02 PM, Chen-Yu Tsai <wens@...e.org> wrote:
> Dithering is a method of approximating a color from a mixture of other
> colors when the required color isn't available. It reduces color
> banding artifacts that can be observed when displaying gradients
> (e.g. grayscale gradients). This may occur when the image that needs
> to be displayed is 24-bit but the LCD panel is a lower bit depth and
> does not perform dithering on its own.
>
> The TCON (LCD controller) found in Allwinner SoCs has hardware support
> for dithering on channel 0, the channel used to feed LCD panels. This
> series adds support for it.
>
> Patch 1 reworks the mode set function for the CPU interface to pass
> the encoder object, so it can be passed to other helper functions.
>
> Patch 2 renames the dithering related register macros to reflect the
> fact that dithering is only supported on channel 0.
>
> Patch 3 adds support for dithering on all LCD panel output types.
>
> Patch 4 adds support for Banana Pi's 7" DPI LCD panel.
>
> Patch 5 adds a pinmux setting for RGB888 for the Allwinner A20 SoC.
> This change has been sent by others before.
>
> Patch 6 provides an example for enabling the Banana Pi 7" DPI LCD panel
> on the Banana Pi M1+. This should not be merged. I will likely rework
> this into an overlay in the future.
>
> Note that I was only able to test dithering with DPI, as I do not have
> other panel types. However the underlying concept and core code is the
> same, as are the drm objects accessed. Nevertheless I'm hoping Jonathan
> can test LVDS and Maxime can test MIPI DSI.
>
> Also it seems pwm-backlight hardware is unusable at the moment. I'm not
> sure whether the pwm-backlight or sun4i-pwm driver is to blame. I had to
> manually poke the pwm registers so the LCD backlight wouldn't be
> completely black.
>
>
> Regards
> ChenYu
>
> Chen-Yu Tsai (5):
>   drm/sun4i: tcon: Pass drm_encoder * into sun4i_tcon0_mode_set_cpu
>   drm/sun4i: tcon: Rename Dithering related register macros
>   drm/panel: simple: Add support for Banana Pi 7" S070WV20-CT16 panel
>   ARM: dts: sun7i: add pinmux setting for RGB888 output for LCD0
>   [DO NOT MERGE] ARM: dts: sun7i: bananapi-m1-plus: Enable Bananapi 7"
>     800x480 RGB LCD panel
>
> Jonathan Liu (1):
>   drm/sun4i: tcon: Add dithering support for RGB565/RGB666 LCD panels

Do you have any working branch to test this, I can't see drm probing
on linux-next, I even enabled de on dts which is missing.

Jagan.