Re: [Qemu-devel] [PATCH v3 5/7] sysbus: Add new platform bus helper device

[Alexander Graf <agraf@suse.de>]

On 26.09.14 14:44, Paolo Bonzini wrote:
> Il 26/09/2014 14:26, Alexander Graf ha scritto:
>>
>> Are you sure? Imagine one sysbus device includes another. We only want
>> to look at the region the lowest sysbus device exposes, no?
> 
> IIUC this function is used to build the device tree.

Yes, it's used to figure out the map of "start of region x of my device"
to "offset y in the platform bus mmio space".

> Say you have 2
> consecutive memory regions and the device tree requires separate "reg"
> entries for them.  But because they are consecutive (or perhaps because
> you have a PCI version of the same device that sticks them in a single
> BAR) you use a single MMIO area at the sysbus level.
> 
> In that case, you will use platform_bus_get_mmio_addr on the two inner
> regions, not the outer one.

In that case, you will use platform_bus_get_mmio_addr on the outer
region because that's what the device model exposes. The parameter to
this function that tells us which region we want is the "mmio region
number" that sysbus exposes.

If in device tree there are 2 reg properties, the device tree assembling
code has to do the conversion from sysbus granularity to device tree
granularity :).

> 
> BTW, I think you will never have one sysbus device including another.
> The contained device would be busless (similar to the "naked" 8250
> device in hw/char/serial.c, except perhaps QOMified).

Yeah, I agree :).


Alex