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

[Chen-Yu Tsai]

Hi,

On Mon, Jan 12, 2015 at 6:18 PM, Hans de Goede <hdegoede at redhat.com> wrote:
> 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).

OK. The Hummingbird uses all 24 bits. The DAC is actually 30 bits.
First I need to get some sort of full color display setup running.
Then I'll do the config options.

>> 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 ?

There's just the regulator that's enabled in u-boot. And I'm not running an
AXP221 enabled kernel either. Hence the weirdness. :|


Regards
ChenYu