Re: [PATCH 1/6] hw/arm: Inline sysbus_create_simple(PL110 / PL111)

[Philippe Mathieu-Daudé]

On 16/2/24 20:54, Philippe Mathieu-Daudé wrote:
> On 16/2/24 18:14, BALATON Zoltan wrote:
> > On Fri, 16 Feb 2024, Philippe Mathieu-Daudé wrote:
> > > We want to set another qdev property (a link) for the pl110
> > > and pl111 devices, we can not use sysbus_create_simple() which
> > > only passes sysbus base address and IRQs as arguments. Inline
> > > it so we can set the link property in the next commit.
> > >
> > > Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> > > ---
> > > hw/arm/realview.c    |  5 ++++-
> > > hw/arm/versatilepb.c |  6 +++++-
> > > hw/arm/vexpress.c    | 10 ++++++++--
> > > 3 files changed, 17 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/hw/arm/realview.c b/hw/arm/realview.c
> > > index 9058f5b414..77300e92e5 100644
> > > --- a/hw/arm/realview.c
> > > +++ b/hw/arm/realview.c
> > > @@ -238,7 +238,10 @@ static void realview_init(MachineState *machine,
> > >     sysbus_create_simple("pl061", 0x10014000, pic[7]);
> > >     gpio2 = sysbus_create_simple("pl061", 0x10015000, pic[8]);
> > >
> > > -    sysbus_create_simple("pl111", 0x10020000, pic[23]);
> > > +    dev = qdev_new("pl111");
> > > +    sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), &error_fatal);
> > > +    sysbus_mmio_map(SYS_BUS_DEVICE(dev), 0, 0x10020000);
> > > +    sysbus_connect_irq(SYS_BUS_DEVICE(dev), 0, pic[23]);
> >
> > Not directly related to this patch but this blows up 1 line into 4 
> > just to allow setting a property. Maybe just to keep some simplicity 
> > we'd rather need either a sysbus_realize_simple function that takes a 
> > sysbus device instead of the name and does not create the device 
> > itself or some way to pass properties to sysbus create simple (but the 
> > latter may not be easy to do in a generic way so not sure about that). 
> > What do you think?
>
> Unfortunately sysbus doesn't scale in heterogeneous setup.

Regarding the HW modelling API complexity you are pointing at, we'd
like to move from the current imperative programming paradigm to a
declarative one, likely DSL driven. Meanwhile it is being investigated
(as part of "Dynamic Machine"), I'm trying to get the HW APIs right
for heterogeneous emulation. Current price to pay is a verbose
imperative QDev API, hoping we'll get later a trivial declarative one
(like this single sysbus_create_simple call), where we shouldn't worry
about the order of low level calls, whether to use link or not, etc.

For the big list of issues we are trying to improve, see:
https://lore.kernel.org/qemu-devel/87o7d1i7ky.fsf@pond.sub.org/