[RFC] arm64: Early printk support for virtio-mmio console devices.

[Will Deacon]

On Fri, Apr 19, 2013 at 10:25:35AM +0100, Pranavkumar Sawargaonkar wrote:
> On 19 April 2013 14:35, Will Deacon <will.deacon at arm.com> wrote:
> > On Thu, Apr 18, 2013 at 09:48:49AM +0100, Pranavkumar Sawargaonkar wrote:
> >> Actually i thought adding a config register will be easier to add a
> >> code than writing entire emulation as 8250 emulation will require to
> >> deal with dealing with more registers and more code.
> >
> > kvmtool already has an 8250 emulation! All we need to do is hack together
> > something which will allow us to instantiate those ioport devices in a more
> > flexible manner (namely, inside the MMIO space for ARM). For earlyprintk, I
> > suspect we can get away without an interrupt too, which should simplify
> > things a bit to start with.
> >
> > Regardless of the outcome of this discussion, I think getting the 8250
> > working on ARM is definitely something worth doing. If I get time, I'll take
> > a look.
> 
> I am not against using 8250 emulation (as far as it solves printk
> issues for kernel booting logs), but my point is why not to add early
> read-write support for virtio console, which also can be useful in
> emulation less mach-virt environment also ?

We can have both, but only one of those requires a change to the virtio
specification.

Will