[PATCH 2/2] drm/sun4i: Handle DRM_MODE_FLAG_**SYNC_POSITIVE correctly
giulio.benetti at micronovasrl.com
Wed Feb 28 07:56:56 PST 2018
Il 16/02/2018 16:50, Maxime Ripard ha scritto:
> On Thu, Feb 15, 2018 at 07:05:56PM +0100, Giulio Benetti wrote:
>>> If so, and if remember the captures properly, the sampling would occur
>>> right before the rise, and not really around the fall.
>>> Would 2/3 be better here?
>> Yes, you're right, 2/3 phase is better:
>> 1/3 phase: https://pasteboard.co/H4VehON.png
>> 2/3 phase: https://pasteboard.co/H4Veq8a.png
>> Take a look at the bit in middle(yellow) sampled by clock(blue).
>> Rising edge is almost in the middle of D0 bit.
>>>> According to scope captures above on both A20 and A33.
>>>> Unfortunately I don't have other boards for the other SoCs to take captures.
>>>> What do you think?
>>> I guess we can make that part applicable to all SoCs, we haven't seen
>>> any significant differences on those part.
>> So let's keep:
>> - As normal(rising edge) => IO_POL_REG "0x2 => 2/3 phase"
>> - As inverted(falling edge) => IO_POL_REG "0x0 => normal phase"
> I was actually thinking 1/3 for rising, 2/3 for falling.
1/3 is almost the same waveform as D0,
having rising an falling edges almost in sync with D0.
It's not so clear because DCLK has a bad figure,
but it is that way.
2/3 instead is almost in the middle of D0 as rising.
- use 0/3 as falling, then DRM_BUS_FLAG_PIXDATA_NEGEDGE
- use 2/3 as rising, then DRM_BUS_FLAG_PIXDATA_POSEDGE
I follow with a new patch using clk_set_phase function.
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