[Letux-kernel] New branches (was Re: jz4780 CI20 v5.8 (was jz4730))

[Paul Boddie]

On Saturday, 18 July 2020 08:45:21 CEST H. Nikolaus Schaller wrote:
> 
> I have now built the kernel (plus my patches with additional printk).
> 
> It boots, enables the display (backlight only). And now handles unplug and
> replug without kernel panic.
> 
> The only thing is that the irq handler is called permanently and triggering
> a lot of activities in the background...

This is probably handling the vblank event, so it might be called quite a lot: 
60 times a second, perhaps. When I have tested it, it seems to me that it does 
eventually stop, however (or is no longer counted in /proc/interrupts).

> I am not sure if it is standard-operation to call e.g.
> drm_atomic_add_encoder_bridges

Off the top of my head - meaning that I am too lazy to check right now - I 
will say that this is probably to be expected. After it is called, you can see 
this getting reported:

dw-hdmi-jz4780 10180000.hdmi: input format 0x100a, output format 0x0001

These values are the "working" defaults (as opposed to uninitialised 
defaults), I think, but they should mean that RGB input and output are set up, 
just as is done for the 3.18 kernel, even though that kernel does things a bit 
differently.

> But I am not sure if it is not introduced by my printk() code which may
> slow down some worker thread too much.

Although the printk probably adds overhead to every frame, I'm not sure it 
would have an impact on the mechanism to the point that initialisation fails. 
That would make the whole arrangement rather too sensitive to timing, I would 
think.

Paul