Re: need help with ACPI generic port implementation for QEMU

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 13 Mar 2023 14:58:42 -0700
Dave Jiang <dave.jiang@intel.com> wrote:

> I'm attempting to implement the support of ACPI "generic port" detailed 
> in the ACPI r6.5 spec in QEMU. The spec section 5.2.16.7 details the 
> Generi Port Affinity Structure where it ties a Device Handle to a 
> Proximity Domain. And with section 6.2.28.4 for the HMAT table, the 
> latency and bandwidth information are provided by the System Locality 
> Latency and Bandwidth Information Structure (SLLBIS) sub-table.
> 
> In the CXL world, a hotplugged type-3 device would not have the 
> approriate end to end latency and bandwidth data provided by the HMAT. 
> The QoS data needs to be computed from the CXL host bridge (HB) and the 
> endpoint device. Some parts of the data are supplemented by the CDAT 
> from the endpoint device and the CXL switch(es) if they exist in the 
> path. The component missing is the path between the CPU and the CXL HB 
> (generic port). The data provided by HMAT for generic port will fill 
> that gap.
> 
> In QEMU, the SRAT is generated by code and the table entry addition is a 
> somewhat straight forward implementation. The HMAT information is fed 
> through user parameter inputs and will require a new object to allow the 
> representation of generic port. The intention is to be able to do 
> something like:
> "-object genport,id=genport0"
> "-numa node,genport=genport0,nodeid=5,initiator=0"
> "-numa dist,src=0,dst=5,val=$dist"
> "-numa 
> hmat-lb,initiator=0,target=5,hierachy=memory,data-type=access-latency,latency=$lat"
> "-numa 
> hmat-lb,initiator=0,target=5,hierarchy=memory,data-type=access-bandwidth,bandwidth=$bw"
> 
> I put together a skeletal generic port device that seems to pass the 
> numa parsing code parts. However I'm hitting an error after that that I 
> can't figure out how to deal with:
> qemu-system-x86_64: ../hw/core/qdev.c:316: 
> qdev_assert_realized_properly_cb: Assertion `dev->realized' failed.
> 
> At what point is qdev_realize() being called for a device object? It 
> seems that this never happens for this generic port device. What am I 
> missing in terms of initialization or setup? Any assistance is 
> appreciated. Thanks in advance. Here's my latest code that I'm playing 
> with as reference:
> https://github.com/davejiang/qemu/tree/genport

Pls, send an RFC series to qemu-devel to start discussion