Re: Nonterministic hang during bootconsole/console handover on ath79

[Antony Pavlov]

On Tue, 22 Mar 2016 00:02:57 +0100
Matthias Schiffer <mschiffer@xxxxxxxxxxxxxxxxxxxx> wrote:

> Hi,
> we're experiencing weird nondeterministic hangs during bootconsole/console
> handover on some ath79 systems on OpenWrt. I've seen this issue myself on
> kernel 3.18.23~3.18.27 on a AR7241-based system, but according to other
> reports ([1], [2]) kernel 4.1.x is affected as well, and other SoCs like
> QCA953x likewise.
> 
> See the log below for the exact place it hangs; the log was taken in during
> a good boot; a bad boot will just hang forever at the marked location. The
> issue is extremely hard to debug, as changing the timing in any way (like
> adding additional printk) will usually make it work without problems. (Even
> recompiling the kernel with the same config, but different uname timestamp
> will make the occurence more or less likely)
> 
> My theory is the following:
> 
> As soon as ttyS0 is detected and installed as the console, there are two
> console drivers active on the serial port at the same time: early0 and
> ttyS0. I suspect that the hang occurs when the primitive early0
> implementation prom_putchar_ar71xx waits indefinitely on THRE,

Can you use EJTAG to prove your theory?

-- 
Best regards,
  Antony Pavlov