Re: JZ4780 LCD controller initialisation (was Re: [PATCH] clocksource: Ingenic: Add high resolution timer support for SMP.)

[Paul Boddie <paul@boddie.org.uk>]

Paul,

Thanks for the reply!

On Tuesday 26. May 2020 17.03.04 Paul Cercueil wrote:
> 
> "lcd0pixclk" and "tve" are for LCD0, "lcd1pixclk" and "lcd" are for
> LCD1.

The 3.0.8 kernel actually uses LCD0 for what the documentation and 3.18 kernel 
call TVE, and it uses LCD1 for what the others call LCD. That earlier kernel 
indicates that LCD1 is the parent clock of LCD0.

I actually found that you can enable LCD0 and not LCD1 and the LCD controller 
(LCDC0) still operates to an extent, but without LCD1 enabled I didn't see a 
DMA command value in the appropriate register, discussed below.

[...]

> OK, indeed the BPP and OSD config is read-only, and it's not a doc
> typo. How annoying.
> 
> I tried to configure the LCD controller for a 8-byte descriptor without
> much success. No IRQs here either.

I had a look at the interrupt controller registers to see whether I was 
missing anything obvious, but the mask was correctly configured to unmask LCD 
interrupts (bit 31 of ICMR0). I did wonder whether the PDMA interrupts might 
need unmasking, just in case there is some interaction between the peripherals 
and that part of the hardware, but unmasking LCD interrupts there (bit 31 of 
DMR0) didn't make any difference.

One observation I can make is that the length or size field of the LCD command 
register (LCDCMD0) does get initialised to the appropriate value as set in a 
descriptor. Since I don't set this register explicitly myself (unlike, I 
think, the current Ingenic DRM driver in the Linux kernel), the value must 
have been set up appropriately by a DMA transfer, as configured using the 
descriptor address register (LCDDA0). However, the command flags I also set in 
the descriptor are not reflected in the register. So, 0x44140000 becomes 
0x00140000.

I thought I should check the interrupt ID register (LCDIID) to see what it 
reveals. Despite setting a value in the appropriate descriptor field, the 
register contains only zero.

I think I must probably tackle the job of initialising the HDMI controller to 
see if that makes a difference. If the interrupts are not working but are also 
not necessary, then maybe I get a visual indication of success.

Thanks for the feedback!

Paul