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Re: [Qemu-devel] Announcing qboot, a minimal x86 firmware for QEMU

From: Dr. David Alan Gilbert
Subject: Re: [Qemu-devel] Announcing qboot, a minimal x86 firmware for QEMU
Date: Wed, 27 May 2015 17:24:18 +0100
User-agent: Mutt/1.5.23 (2014-03-12)

* Paolo Bonzini (address@hidden) wrote:
> On 26/05/2015 23:25, Christopher Covington wrote:
> > On 05/25/2015 08:53 AM, Paolo Bonzini wrote:
> >>
> >> On 22/05/2015 13:12, Daniel P. Berrange wrote:
> >>> In
> >>> particular I don't see why we need to have a SATA controller and ISA/LPC
> >>> bridge in every virt machine - root PCI bus only should be possible, as 
> >>> you
> >>> can provide disks via virtio-blk or virtio-scsi and serial, parallel, 
> >>> mouse,
> >>> floppy via PCI devices and/or by adding a USB bus in the cases where you
> >>> really need one.
> >>
> >> I think removing the ISA/LPC bridge is hard.  It includes the real-time
> >> clock and fw_cfg, for example.
> > 
> > Could VirtIO specified replacements make sense for these peripherals?
> Not really.  virtio is too heavyweight and you'd be reinventing the
> wheel unnecessarily.

I see reasons to replace some but not all these components;  and there's no 
in replacing the ISA/LPC bridge since it's got nothing at all in it.

> For example, ARM's "-M virt" uses a pl011 block for the RTC, and also
> uses fw_cfg.  Another commonly used ISA device is the UART, for which
> again -M virt uses a pl031.

I don't see much point in replacing the simple PC uart with
anything virtio; I can imagine that you might want to go down
to something really trivial with non of the bells and whistles;
but a UART is pretty simple.

The PC RTC though, it's a bit of a disaster that's had 30 years
of random cruft added into it to hold random things that should never
have been there.


> Paolo
Dr. David Alan Gilbert / address@hidden / Manchester, UK

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