Re: [PATCH v7 08/17] cxl/pci: Map CXL PCIe Upstream Switch Port RAS registers

[Dan Williams]

Terry Bowman wrote:
> Add logic to map CXL PCIe Upstream Switch Port (USP) RAS registers.
> 
> Introduce 'struct cxl_regs' member into 'struct cxl_port' to cache a
> pointer to the CXL Upstream Port's mapped RAS registers.
> 
> Also, introduce cxl_uport_init_ras_reporting() to perform the USP RAS
> register mapping. This is similar to the existing
> cxl_dport_init_ras_reporting() but for USP devices.
> 
> The USP may have multiple downstream endpoints. Before mapping RAS
> registers check if the registers are already mapped.

Yes, now this sharing makes sense, but the ras_init_mutex +
cxl_init_ep_ports_aer() approach to solving it is broken.

> Introduce a mutex for synchronizing accesses to the cached RAS
> mapping.

In this case, especially for VH configs, you should just be able to map
the RAS registers once from cxl_endpoint_port_probe(). That will
naturally only be called once when the first endpoint arrives, and will
never be torn down until the last cxl_detach_ep() event triggers
delete_switch_port().