[U-Boot] [PATCH 0/3] sunxi: Enable VGA output on Hummingbird A31

[Hans de Goede]

Hi,

On 12-01-15 11:02, Chen-Yu Tsai wrote:
> Hi Hans, Ian,
>
> This series enables the VGA output on the Hummingbird A31. The VGA output
> is driven from LCD0, through an external DAC that's powered up by toggling
> pin PH25.

Thanks for working on this!

> Patch 1 allows selecting CONFIG_VIDEO_VGA_VIA_LCD on sun6i and sun8i.
> These 2 platforms do not have builtin TV encoders, and some vendor may
> use an external DAC to support VGA.
>
> Patch 2 adds support for toggling a GPIO pin as part of the video init
> sequence to power up the DAC
>
> Patch 3 updates the Hummingbird A31 defconfig to enable VGA output.
>
> I have one question about the VGA_VIA_LCD code in general. The color depth
> is forced to 18. Is this necessary?

Depends on the DAC-s you're using, so far this was only used with Olinuxino
boards which use 6 bits dacs. If your board has 8 bit dacs then we should
make this configurable. Note that all this does is enable dithering to avoid
color gradients becoming ugly with 6 bits dacs, but with 8 bit dacs we should
disable the dithering (which is done when depth == 24).

> Can we make it configurable? I haven't
> tried displaying pictures so I don't know if it makes a visible difference.
>
> Also with the VGA output on my Hummingbird A31, I get greenish flashing
> pixels where it should be black, like in and between characters. Once
> booted in to the kernel this disappears, and I get a nice console with
> simplefb. Kind of weird.

Weird indeed, could it be that the DAC-s need some power-supply setup which
u-boot does not set up, but your axp221 kernel code does setup ?

Regards,

Hans