Re: Questions about the qemu DCD support in cxl-2023-09-13

[fan <nifan.cxl@gmail.com>]

On Thu, Sep 21, 2023 at 03:24:26PM -0700, Ira Weiny wrote:
> Fan,
> 
> I'm working off of Jonathan's latest CXL branch with the DCD patches.[1]
> 
> I've been testing various things and so far I have a couple of questions.
> 
> 1) If the qmp command is used to add extents which overlap other extents
>    shouldn't that throw an error?  I don't see any validation of this and
>    I would think a real device would reject such a request from the FM.
> 
> 2) Where is CXLType3Dev->dc.total_extent_count set?  Attempting to add
>    extents prior to driver load does not seem to work.  And I think this
>    is because total_extent_count is 0 in cmd_dcd_get_dyn_cap_ext_list().
> 
> Ira
> 
> [1] https://gitlab.com/jic23/qemu/-/tree/cxl-2023-09-13

Hi Ira,
FYI. I have updated the DCD emulation patch series based on feedbacks on
the previous version.

The new version is here:
https://github.com/moking/qemu-jic-clone/tree/dcd-dev

The code is based on Jonathan's branch cxl-2023-09-26.

The main changes include,

1. Update cxl_find_dc_region to detect the case the range of
the extent cross multiple DC regions.
2. Add comments to explain the checks performed in function
cxl_detect_malformed_extent_list. (Jonathan)
3. Minimize the checks in cmd_dcd_add_dyn_cap_rsp.(Jonathan)
4. Update total_extent_count in add/release dynamic capacity response function.
(Ira and Jorgen Hansen).
5. Fix the logic issue in test_bits and renamed it to
test_any_bits_set to clear its function.
6. Add pending extent list for add/release extent event.
7. When add/release extent response is received, use the pending list to
verify the extents are valid.
8. Add test_any_bits_set and cxl_insert_extent_to_extent_list declaration to
cxl_device.h so it can be used in different files.
9. Updated ct3d_qmp_cxl_event_log_enc to include dynamic capacity event log type.
10. Extract the functionality to delete extent from extent list to a helper
function.
11. Move the update of the bitmap which reflects which blocks are backed with
dc extents from the moment when a dc extent is offered to the moment when it
is accepted from the host.

I was able to test the DCD code you sent previously, let me know if you
find any issues.

Fan