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

[Fan Ni <fan.ni@samsung.com>]

On Thu, Sep 21, 2023 at 03:24:26PM -0700, Ira Weiny wrote:

Hi Ira,

Thanks for reaching out.
For DCD, I think Jonathan's branch does not change much compared to the patch
series sent out except some obvious issues that blocks the test.

My initial plan was to update the patches after I have tested the
current version with more stable kernel DCD driver.

See below.


> 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.
> 

Yes. We do not have any validation for the overlapped extents here
in current code.

> 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().

I am aware of the issue, yet have not got a chance to fix it. 

My understanding is whenever we complete adding/releasing
extents, we update it.

I will fix it and other issues mentioned in the comments in the next version.

Fan
> 
> Ira
> 
> [1] https://urldefense.com/v3/__https://gitlab.com/jic23/qemu/-/tree/cxl-2023-09-13__;!!EwVzqGoTKBqv-0DWAJBm!WrndoKsXHVaUoln-Jsq7MFRemLlcFYg788t_tDaFt1lS7WFhE2s_5hsI4-WuNzlgLOc0e0DgdcepR368SHU$