On Wed, Apr 9, 2014 at 6:02 PM, Markus Armbruster <arm...@redhat.com> wrote: > Alistair Francis <alistair.fran...@xilinx.com> writes: > >> On Wed, Apr 9, 2014 at 11:28 AM, Peter Crosthwaite >> <peter.crosthwa...@xilinx.com> wrote: >>> On Wed, Mar 26, 2014 at 10:47 AM, Alistair Francis >>> <alistair.fran...@xilinx.com> wrote: >>>> This patch introduces a new command line argument that allows >>>> sysbus devices to be attached via the command line. >>>> >>>> This allows devices to be added after the machine init but >>>> before anything is booted >>>> >>>> The new argument is -sysbusdev >>>> >>>> A new argument is being used to avoid confusion and user >>>> errors that would appear if the same command for hot-plugging >>>> was used instead. This could be changed to use -device and >>>> specify sysbus by using something like 'bus=sysbus' if that >>>> is preferred >>>> >>> >>> Can you be more specific about the confusion issue you are seeing? If >>> you went for -device bus=root (meaning the default singleton root >>> sysbus), where are the possible issues? >>> >> >> Using -device would be possible (and easy to implement). The reason I >> started with >> a different argument name was just to avoid confusion and to make sure >> I didn't interfere with hot-pluggable devices. I still feel that separating >> hot-pluggable devices from bus devices is a good idea. They are initialised >> in slightly different parts of the code (although this wouldn't >> be hard to fix). The name 'sysbusdev' is confusing though, as it doesn't >> have to connect to the sysbus. > > -device / device_add already covers both hot plug and cold plug. In > fact, only device_add can hot plug; all -device ever does is cold plug. > > Plugging in a device involves wiring it up. Hot plug additionally > involves communication with guest software, but let's ignore that for > now. > > -device uses generic wiring code, guided by configuration: property > "bus". This suffices for straightforward cases like PCI and USB > devices. It doesn't for sysbus devices, because these may require > arbitrarily complex wirings. Therefore, sysbus devices are unavailable > with -device; see commit 837d371. > > What we need is a way for configuration to guide more general wiring. > Perhaps -device can be extended. If that turns out to be impractical, > we need something more expressive that also covers everything -device > does now, and can cover "everything" eventually. Andreas may have ideas > here.
I have managed to extended -device to allow QOM devices to be attached to the system bus. I removed the -sysbusdev argument and am now back to just using "-device" where the user can specify which bus to connect to. This allows entire machines to be built from command line arguments using "-M none". I'm just tidying up the patch now > > What we don't need, in my opinion, is more special-case options :) > > [...] >
