Re: CXL Namespaces of ACPI disappearing in Qemu demo

["Yuquan Wang" <wangyuquan1236@phytium.com.cn>]

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Hi, Jonathan
On 2023-09-04 20:43,  jonathan.cameron wrote:
> 
> At the system design level, MMIO space of Root complex register space via RCRB
> does not map in a similar fashion to PCIE MMIO space (which is handled via
> address decoding in the PCIE fabric). It is much more similar to MMIO for platform
> devices - as such the implementation handles in like a platform device (well 16 of
> them which seemed enough for any sane usecase).
> 
> 

Oh,thanks! According to above, therefore, the core factor is the implementation of RCRB.

> 
> So in theory we could make some space for the CXL root bridge RCRB registers
> but it would make various generic paths more complex.  In a real system
> those registers are likely to be far from the PCI MMIO space anyway so the
> way it's modeled is probably more realistic than pushing the RCRB into the
> existing allocation.
> 

Here implies that all CXL root bridge will use RCRB registers.

From Table 8-17 and Figure 9-14 in CXL3.0 specification, I understood that only RCH DP &
RCD UP will use RCRBs, and CXL host bridges VH mode will use other way to realize
the CHBCR. I had tried to find more explanation in CXL spec, but I haven't found. Hence 
this is why I am confused.

Many thanks
Yuquan

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