[Letux-kernel] jz4730-i2c - clocksource

[H. Nikolaus Schaller]

Hi Paul,

> Am 06.03.2021 um 22:56 schrieb Paul Boddie <paul at boddie.org.uk>:
> 
> On Saturday, 6 March 2021 18:12:48 CET H. Nikolaus Schaller wrote:
>> 
>> Now there is also letux-current which is the latest complete tree that I did
>> build and test.
> 
> So, I built the letux-current kernel and hopefully installed all the modules 
> in a fresh Debian Stretch root ext2-formatted filesystem, with the uImage in 
> its normal place on the primary FAT-formatted partition. Unfortunately, I 
> still don't get anything shown on the screen whose backlight does come on (as 
> usual).

You might try to download my binary builds and replace uImage or modules or DTB
to check where the difference is.

https://download.goldelico.com/letux-kernel/latest-l400/

And, which defconfig did you use? I use the letix_mipsbook_defconfig.
The alpha400_defconfig may be incomplete for LCD.

> 
> [...]
> 
>> But what would happen if cpu_has_llsc is wrongly defined as "1"? Shouldn't
>> this trigger some ILLEGAL INSTRUCTION fault in kernel and perhaps panic
>> the kernel?
> 
> I imagine that it should be trapped and even emulated at some level. That 
> might not seem to make much sense, given that the aim of using LL/SC is to 
> avoid expensive transitions to kernel space, but if a program uses it then 
> there has to be a way of supporting it.
> 
> The futex implementation seems to return an error code if it is invoked 
> without LL/SC support, so the kernel presumably does not use the instruction 
> if it is missing. However, if it does not know it is missing, maybe some 
> emulation occurs that ends up being rather expensive within the kernel itself.

Ok, at least something we can try to analyse.

> 
>>> So it is possible that LL/SC support is missing and that this flag might
>>> be unset for better performance. But that is just an idea.
>> 
>> We should give it a try...
> 
> If I can get the kernel working, then I might see what effect it has.


Yes.

BR,
Nikolaus