Re: [Qemu-devel] [GSoC?] Board autoconfiguration based on DTB info

[Stefan Hajnoczi]

On Mon, Jan 22, 2018 at 05:59:00PM +0000, Peter Maydell wrote:
> On 22 January 2018 at 17:52, Alexander Monakov <address@hidden> wrote:
> > Is it feasible to consume a DTB file in Qemu itself to make the board match 
> > the
> > DeviceTree hardware description? For example on Arm there are quite a few 
> > .dts
> > files in Linux tree for various boards; having a "generic" Arm board in 
> > Qemu that
> > could [to what degree?] emulate any of those sounds attractive in theory.
> 
> This is an idea that people have suggested before, and it's certainly
> an attractive theory, but unfortunately it doesn't work. The dtb files
> contain enough information about the hardware to allow an OS (and in
> particular Linux) to boot, but they don't include enough information
> in all cases to allow QEMU to create the hardware in the correct way.
> 
> (There are some specialized situations where you can do it, for
> instance if you're an SoC manufacturer and you're creating both
> hardware and DTB and QEMU model yourself you can ensure that they're
> all consistent and generated from the same original information and
> the DTB has all the info QEMU needs in it; but we can't do it upstream
> in the general case.)
> 
> Also, the main reason we don't have support for a wider range of Arm
> boards is that all the devices are different -- it's no good being
> able to read a dtb file that says there is a "mediatek,mt6797-uart" at
> a particular address if we don't actually have a model of that UART.
> Once you have all the device models, wiring up the SoC and board
> level code in QEMU isn't really all that difficult (though we could
> probably manage to make it a bit less boiler-platy).

Thanks for explaining.

Alexander: Thanks for raising the idea for discussion!  If you have
anything else, please don't hesitate to post on qemu-devel.

Stefan

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