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Re: [Qemu-devel] [PATCH v2 1/4] Add i.MX FEC Ethernet driver

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH v2 1/4] Add i.MX FEC Ethernet driver
Date: Mon, 6 May 2013 11:51:06 +0300

On Sun, May 05, 2013 at 11:00:24PM +0100, Peter Maydell wrote:
> On 5 May 2013 22:15, Michael S. Tsirkin <address@hidden> wrote:
> > On Sun, May 05, 2013 at 07:01:34PM +0100, Peter Maydell wrote:
> >> Sorry, you can't say this until we've sorted out the mess
> >> that is new-style networking options in a machine which
> >> creates embedded network controllers.
> > What is missing exactly?
> > Could you please give some examples of the problems
> > that -netdev + -device has but -net does not have?
> -netdev + -device is fine (unsurprisingly since that's the
> PC usecase); -netdev + a device that's preinstantiated by the
> board is not so fine. And you can't use -device to instantiate
> most embedded network controllers because there's no way to
> wire up the IRQs and MMIOs.

Can't board code look for instanciated controllers
and wire them up?

> There's probably a nasty workaround involving '-global', but:
>  * that requires the user to know the device name for the
>    onboard NIC for the board, which is a regression from
>    the -net situation
>  * it's not clear how it works if the board has two NICs
>    of the same type

How does it work now?
I am guessing each -net nic gets mapped to a random device.
At some level that's worse than documenting about internal names,
we are teaching users to learn order of initialization
by trial and error and then rely on this.

>  * if we claim -global is the right approach we need to actually
>    document it (and document all the board NIC names, yuck)
>  * we need to fix existing boards which do the "don't instantiate
>    NIC unless the user said -net nic" trick by looking at
>    nd_table[]
>  * we need to make the board code pass the right NIC properties
>    in both the "legacy -net option" and "new style" cases (at the
>    moment, for instance, lan911_init() insists on having a
>    NICInfo* passed to it)
> -net nic works for these use cases because it will operate on
> the NICs created by the machine models, because the machine
> models look at the nd_table[] when they create the NICs.
> thanks
> -- PMM


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