[Letux-kernel] jz4780 read out LCDC setup for HDMI

Maarten ter Huurne maarten at treewalker.org
Sat Jun 6 02:15:29 CEST 2020

On Friday, 5 June 2020 22:48:13 CEST Paul Boddie wrote:

> One obstacle previously mentioned was that of end-of-frame interrupts.
> Having configured those in my test environment, I can indeed receive
> these interrupts (or at least some kind of interrupt condition) at a
> frequency that suggests that the end-of-frame condition is causing
> interrupts to be delivered. In other words, I can count 60 of them
> every second or so. Therefore, it should be possible to get the LCD
> controller into an appropriate state to pass the "vblank" test,
> although I imagine that the initialisation sequencing still remains a
> challenge: the HDMI peripheral may need to be active first, but there
> may be expectations of an input signal being available before the
> HDMI peripheral is activated; something will need to short-circuit
> any such logic.

On the JZ4770 we found that end-of-frame interrupts would occur when the 
DMA descriptor had been processed instead of when the transfer ends. We 
put a dummy black line in a second DMA descriptor chained after the 
first one and used that to detect the end of the frame.

I don't know if the JZ4780 does the same thing, but in general the SoCs 
in the series have more similarities than differences.


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