On 04/10/2024 14.40, Jonathan Cameron wrote: > External email: Use caution opening links or attachments > > >>> >>>> >>>> Presumably, the host creates one large CXL region that covers the entire >>>> DPA, while QEMU can virtually partition it into different regions and >>>> map them to different virtual CXL region if QEMU presents multiple HDM >>>> decoders to the guest. >>> >>> I'm not sure why it would do that. Can't think why you'd break up >>> a host region - maybe I'm missing something. >>> >> >> It is mostly concerning about a device can have multiple HDM decoders. >> In the current design, a large physical CXL (pCXL) region with the whole >> DPA will be passed to the userspace. Thinking that the guest will see >> the virtual multiple HDM decoders, which usually SW is asking for, the >> guest SW might create multiple virtual CXL regions. In that case QEMU >> needs to map them into different regions of the pCXL region. > > Don't let the guest see multiple HDM decoders? > > There is no obvious reason why it would want them other than type > differences. > > Why is it useful for a type 2 device to be setup for multiple CXL regions? > It shouldn't be a performance thing. Might be convenient for management > I guess, but the driver can layer it's own allocator etc on top of a single > region so I'm not sure I see a reason to do this... > Sorry for the late reply as I were confirming the this requirement with folks. It make sense to have only one HDM decoder for the guest CXL type-2 device driver. I think it is similar to efx_cxl according to the code. Alejandro, it would be nice you can confirm this. Thanks, Zhi. > Jonathan > >
