[Letux-kernel] [PATCH 00/20] A bunch of JZ4730 fixups for letux-kernel

[Paul Boddie]

On Saturday, 5 December 2020 22:35:15 CET Paul Boddie wrote:
> On Saturday, 5 December 2020 22:19:01 CET Paul Boddie wrote:
> > So, what we might want to provide in the device tree is this:
> > 
> > reg = <0x10020000 0xc0>, <0x100200f8 0x08>;
> 
> [...]
> 
> > So, what probably needs to be done is some parameterisation to use the
> > right offsets for descriptor address registers and the principal global
> > registers. Meanwhile, some investigation into what might be used for the
> > doorbell registers might be needed. Where other peripherals manipulate the
> > DMA system, I don't think the doorbell mechanism is needed at all, though.
> 
> For the time being, here's a tentative patch for the driver. The device tree
> will also need modifying as noted above.

Here, I actually misunderstood the JZ4730 definitions: there doesn't actually 
seem to be transfer descriptor support in the JZ4730 at all. Looking at the 
legacy kernel sources generally gives this impression, but the lack of a 
dedicated command register, to which the descriptor will correspond, is the 
principal clue otherwise.

What I interpreted as the descriptor address register (DA) is probably the 
"destination" address register, otherwise known as the target address register 
(TA). This probably also explains the lack of any "doorbell" registers in the 
JZ4730. So, the global registers are the only ones of consequence that differ.

Consequently, I will have to rework this patch to try and support explicitly-
invoked transfers. Sorry for any inconvenience or extra effort for no reward!

Paul