[Lenny400] [Letux-kernel] JZ4730/Minibook framebuffer driver updates

[H. Nikolaus Schaller]

Hi Daniel,

> Am 10.09.2017 um 19:55 schrieb Daniel Glöckner <daniel-gl at gmx.net>:
> 
> Hi,
> 
> On Sun, Sep 10, 2017 at 07:31:44PM +0200, H. Nikolaus Schaller wrote:
>> Let's think about where limitations could be...
>> 
>> 1. the total card size may be limited by file system but FAT and ext can
>>   handle big file systems
>> 2. the raw MMC driver treats the card as single big file with partitions
>>    - but there I am not aware of limits
>> 3. the partition manager might ot be able to handle big partitions - but
>>   this works well on ARM - why should MIPS be different?
>> 4. there might be a limit in the MMC controller inside the JZ4730 and the
>>   raw MMC driver that it can't send big block addresses automatically.
>>   It would only a problem if the MMC controller has e.g. a 16 or 24 bit
>>   register for block address and there is a "read block" command and
>>   everything else is done by DMA. Then, an old controller can never send
>>   "extended" addresses going beyond the card's capabilities to the card.
> 
> 5. The U-Boot that we don't dare to replace might be too old to load the
>   kernel from an SDHC card.

Ah, yes. That could happen.

But is quite unlikely. There is a first FAT partition which contains the uImage
and that is everything which should be loaded. I'd expect that as long as the
first partition is small enough, U-Boot will even find it on the first sectors
of an SDXC card.

> I've been following the recent activities on this mailing list and I really
> hope it will lead to mainline support for this device. But did I understand
> correctly that all of the work so far has been done without booting the new
> kernel?

Yes :)

I still have to remove dust from my devices (one is still missing) and find
out which ones are still booting from flash with the built-in 2.4 kernel.

Next I have to add the uart interface to watch the boot console.

And before booting the 2.6.24, I have to flash a working old SD card first :)

And then we will see if we can get a mainline kernel running...

Best expectation is that we see

Starting kernel...
[0.00000] first messages
...

and then something hangs or emits warnings, errors or kernel panics. Then
printk() becomes our best friend :)

Worst expectation is that we do not see anything after 
Starting kernel...

This is more difficult, but not impossible to debug (even without JTAG). I
had that on the GTA04 several times during our long journey towards latest
Letux kernels.

But IMHO chances are not thad bad. I looked through Paul's code and although
I did not understand everything and have not compared, he has basically mixed
things from the older 2.6.24 kernel and modern (and tested) jz4740/80 code.

So I'd expect the mix to be 80% correct and less than 20% wrong...

BR,
Nikolaus