Skip to content

sunxi: Enable VGA output on Hummingbird A31

Hans de Goede u-boot 1 version New

Get series with b4
b4 am [email protected]

Versions newest first

  1. v1 Latest1 of 3 patches 0 repliesNew

1 of 3 patches is in this archive. The cover letter announces 3.

Patches in v1 No applies recorded yet

#Subject and filesSizeRepliesApplied
2/3sunxi: video: Add support for external DAC enable pin+0 -01 reply

Reviews trailers per patch

No Reviewed-by, Acked-by or Tested-by trailers for v1 yet.

Read the v1 thread

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

Hi,

Quoted 5 lines · Chen-Yu Tsai

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!

Quoted 11 lines

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).

Quoted 7 lines

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

Read the cover letter in its thread