Re: [Qemu-devel] [PATCH v6 0/2] hw/arm: add 'virt' platform

[Peter Maydell]

On 14 August 2013 09:52, Alexander Graf <address@hidden> wrote:
> On 13.08.2013, at 14:03, Peter Maydell wrote:
>> An obvious thing this machine does not provide is a serial
>> port. I would rather just use virtio-console (and we
>> should implement the 'emergency console/earlyprintk' bit of
>> the virtio spec).
>
> Are you sure about this?

Nope, which is why I flagged it up in the commit message.
"No UART" is the idealistic approach, but maybe it won't work...

> Not implementing a UART / something more
> standardized has been an absolute nightmare on s390. Device names
> diverge, so distributions get confused

Device names are all over the shop for ARM serial ports anyway:
no two boards are the same. (This is a Linux kernel general
design flaw -- "first serial port" should be the same /dev/
name regardless of actual hardware/driver implementing it.)
That said, "we tried this on s390 and it was a mistake" is a
pretty good argument.

> and there's this nasty bug
> somewhere in virtio-console that makes your input lag when you enter
> a lot of data quickly on the port.
>
> I would really prefer to just define a UART for this machine. It
> will make life a lot easier.

UARTs are awkward because you have to get into defining clocks
for them in the device tree as far as I can see. And you still
have the problem that the kernel doesn't know where they are
for earlyprintk purposes.

-- PMM