Re: [RFC 1/4] memory: add memory_region_init_io_with_dev interface

[Li Qiang]

Alexander Bulekov <alxndr@bu.edu> 于2020年9月9日周三 下午10:28写道：
>
> On 200909 1258, Li Qiang wrote:
> > Gerd Hoffmann <kraxel@redhat.com> 于2020年9月9日周三 下午12:49写道：
> > >
> > > On Wed, Sep 09, 2020 at 10:15:47AM +0800, Jason Wang wrote:
> > > >
> > > > On 2020/9/9 上午12:41, Li Qiang wrote:
> > > > > Currently the MR is not explicitly connecting with its device instead 
> > > > > of
> > > > > a opaque. In most situation this opaque is the deivce but it is not an
> > > > > enforcement. This patch adds a DeviceState member of to MemoryRegion
> > > > > we will use it in later patch.
> > > >
> > > >
> > > > I don't have a deep investigation. But I wonder whether we could make 
> > > > sure
> > > > of owner instead of adding a new field here.
> > >
> > > Should be possible.  There is object_dynamic_cast() which can be used to
> > > figure whenever a given owner object is a device.
> > >
> >
> > I found most caller of 'memory_region_init_io' will set the owner to
> > the device object.
> > But some of them will just set it to NULL. Do will have a clear rule
> > that the device's MR
> > 'owner' should be the device object? If yes, we can use this field.
> >
>
> Those seem to be devices that havent't been QOM-imfied yet?  Maybe those
> devices are unlikely to be affected by these issues, though...
>

No it seems not related QOM-ified.

> For i386, it seems like parallel, port80, portF0, pckbd, and xen_pvdevice .. ?
> I'm guessing none of these do DMA.
>

In fact xen_pvdevice is MMIO but the handlers does nothing.

There are some other example than i386 such as the riscv in
hw/riscv/sifive_uart.c

If we have a rule to force the 'MR's owner to the device then we can
fix these NULL owner MR.

Thanks,
Li Qiang

> +CC Stefan, since he replied to the other thread.
>
> > Thanks,
> > Li Qiang
> >
> > > take care,
> > >   Gerd
> > >