SRU Justification:
Impact: earlyprintk doesn't work in mach-virt (qemu guest target for kvm on arm) because at boot time, the clock necessary to make pl011 serial port running is not added via device tree (and thus the serial console is not probed) - also see https://lists.gnu.org/archive/html/qemu-devel/2013-10/msg02427.html.
Fix: apply the attached patches and recompile a kernel.
Test case: try booting a patched (and an unpatched kernel) in kvm guest passing earlyprintk and NO console, and see if it emits any output.
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There is no earlyprintk via the PL011 because there's no defined device tree binding for earlyprintk UART to get the PL011 to work you'll need to tweak the kernel a bit. kernel doesn't ever add the clock to its list, and then it refuses to probe for the PL011. This is a temporary fix, ideally the call should be done in some generic location rather than in every machine's init function.) The alternative would be for the kernel to be fixed to follow its own device tree binding documentation and not require clocks/clock-names properties on the pl011 node.
This patch is a temporary fix.