Re: [RFC PATCH v5 0/3] Sysbus device generic QAPI plug support

[Damien Hedde <damien.hedde@greensocs.com>]

On 5/30/22 12:25, Peter Maydell wrote:
> On Mon, 30 May 2022 at 10:50, Damien Hedde <damien.hedde@greensocs.com> wrote:
>> TYPE_SYS_BUS_DEVICE also comes with reset support.
>> If a device is on not on any bus it is not reached by the root sysbus
>> reset which propagates to every device (and other sub-buses).
>> Even if we move all the mmio/sysbus-irq logic into TYPE_DEVICE, we will
>> still miss that. The bus is needed to handle the reset.
>> For devices created in machine init code, we have the option to do it in
>> the machine reset handler. But for user created device, this is an issue.
> 
> Yes, the missing reset support in TYPE_DEVICE is a design
> flaw that we really should try to address.
> 
>> If we end up putting in TYPE_DEVICE support for mmios, interrupts and
>> some way to do the bus reset. What would be the difference between the
>> current TYPE_SYS_BUS_DEVICE ?
> 
> There would be none, and the idea would be to get rid of
> TYPE_SYS_BUS_DEVICE entirely...
> 

Do you expect the bus object to disappear in the process (bus-less 
system) or transforming the sysbus into a ~TYPE_BUS thing ?

Assuming we manage to sort out this does cold plugging using the 
following scenario looks ok ? (regarding having to issue one command to 
create the device AND some commands to handle memory-region and 
interrupt lines)

 > device_add driver=ibex-uart id=uart chardev=serial0
 > sysbus-mmio-map device=uart addr=1073741824
 > qom-set path=uart property=sysbus-irq[0] value=plic/unnamed-gpio-in[1]

TYPE_DEVICE or TYPE_SYS_BUS_DEVICE, my goal is still to be able to 
cold-plug a "ibex-uart" define its memory map and choose which irq I 
wire where.

Thanks,
Damien