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

[H. Nikolaus Schaller]

Hi Paul,

> Am 11.12.2020 um 01:52 schrieb Paul Boddie <paul at boddie.org.uk>:
> 
> 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!

No, there was already reward because it made the jz4370 dma succeed in probe.
Even if it is still wrong we would not have found other minor issues.

What I think we should also try to identify is why the MMC is not detected at
all. At least there should be some indication, even if DMA can not read.

This could be an gpio or regulator or mmc-host driver issue.

If I find time for a debug session I could try to find how card insert detection
works and if it works...

BR and thanks,
Nikolaus