On Wed, Jan 24, 2018 at 08:37:28PM +0100, Giulio Benetti wrote:

quoted

quoted

quoted

Also, how was it tested? This seems quite weird that we haven't caught
that one sooner, and I'm a bit worried about the possible regressions
here.

It sounds really strange to me too,
because everybody under uboot use "sync:3"(HIGH).
I will retry to measure,
unfortunately at home I don't have a scope,
but I think I'm going to have one soon, because of this. :)

Here I am with scope captures and tcon0 registers dump:
tcon0_regs => https://pasteboard.co/H4r8Zcs.png
dclk_d0 => https://pasteboard.co/H4r8QRe.png
dclk_de => https://pasteboard.co/H4r8zh4R.png
dclk_vsnc => https://pasteboard.co/H4r8Hye.png

As you can see circled in reg on registers,
TCON0_IO_POL_REG = 0x00000000.
But on all the waveforms you can see:
- dclk_d0: clock phase is 0, but it starts with falling edge, otherwise
the rising front overlaps dclk rising edge(not good), so to me this is
falling, then I mean it Negative.
- dclk_de: de pulse is clearly negative, even if register is 0 and its'
polarity bit is 0.
- dclk_vsnc: same as dclk_de
- dclk_hsync: I didn't take scope screenshot but I can assure you it's
negative.

You can also check all the other registers about TCON0.

Now I proceed testing it on A33, maybe the peripheral is slightly
different between Axx SoCs, if I find it that way,
it should be only a check about SoC or peripheral ID,
and treat polarity as it should be done.

Here I am with A33 waveforms:
tcon0_regs => https://pasteboard.co/H4rXfN0M.png
dclk_d0 => https://pasteboard.co/H4rVXwy.png
dclk_de => https://pasteboard.co/H4rWDt8.png
dclk_vsnc => https://pasteboard.co/H4rWRACu.png
dclk_hsync => https://pasteboard.co/H4rWK6I.png

It behaves the same way as A20, so as I mean IO polarity,
all signals(except D0-D23), are inverted.
For A33 I've used A33-OLinuXino.
For A20 our LiNova1.

If you have an A33 handy, you probably want to read that mail:
https://lists.freedesktop.org/archives/dri-devel/2017-July/147951.html

Especially the 90-phase part.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
http://bootlin.com
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