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