aarch64: earlyprintk not properly enabled

[Brian Foley (ARM)]

On the arm64 port, if you don't provide name and address parameters to the earlyprintk command line option, it doesn't try to probe for a UART and doesn't give you an early console.

The vexpress and foundation model kernel images have the default command line 'console=ttyAMA0 root=XXX earlyprintk consolelog=9 rw'. For early console output to display, this should be changed to 'console=ttyAMA0 root=XXX earlyprintk=pl011,0x1c090000 consolelog=9 rw'.

[Marcin Juszkiewicz (hrw)]

I booted linux-linaro 3.9-rc2 with "earlyprintk=pl011,0x1c090000" and did not noticed any difference.

[Fathi Boudra (fboudra)]

Brian, any comments? Otherwise, we'll close the bug.

[Brian Foley (ARM) (brian-foley-arm)]

Hi Marcin,

it's mostly only noticable if you're trying to debug or measure something early in the boot process after the kernel has started printk-ing messages, but before the uarts listed in the device tree have been initialised.

It caused me problems when I was trying to debug a regression with the generic timers (in the models) that was causing the secondary core bringup to fail and to fail to timeout. Without the earlyprintk, nothing was ever printed to the console.

It would be similarly useful when trying to boot linux on an extremely slow system such as RTL simulation, emulation, or FPGA.

[Marcin Juszkiewicz (hrw)]

OpenEmbedded kernels will use this.

Will it be used for kernels built by CI? No idea.

[Fathi Boudra (fboudra)]

Set to fix-commited. It isn't fix-released until the fix reached official images published on releases.linaro.org.

[Marcin Juszkiewicz (hrw)]

Fathi: where your CI build finds information about kernel cmdline?

[Marcin Juszkiewicz (hrw)]

https://git.linaro.org/gitweb?p=ubuntu/linux-linaro-raring.git;a=commitdiff;h=3cc2518196dc30a1644ea43e0826f7a81732391e;hp=ea679a990ae704bcd704817954aef60a9e0c9698