Re: [PATCH v2 06/12] cxl/memdev: Make mailbox functionality optional

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Thu, 15 Jun 2023 14:30:35 -0700
Dave Jiang <dave.jiang@intel.com> wrote:

> On 6/14/23 18:30, Dan Williams wrote:
> > In support of the Linux CXL core scaling for a wider set of CXL devices,
> > allow for the creation of memdevs with some memory device capabilities
> > disabled. Specifically, allow for CXL devices outside of those claiming
> > to be compliant with the generic CXL memory device class code, like
> > vendor specific Type-2/3 devices that host CXL.mem. This implies, allow
> > for the creation of memdevs that only support component-registers, not
> > necessarily memory-device-registers (like mailbox registers). A memdev
> > derived from a CXL endpoint that does not support generic class code
> > expectations is tagged "CXL_DEVTYPE_DEVMEM", while a memdev derived from a
> > class-code compliant endpoint is tagged "CXL_DEVTYPE_CLASSMEM".
> > 
> > The primary assumption of a CXL_DEVTYPE_DEVMEM memdev is that it
> > optionally may not host a mailbox. Disable the command passthrough ioctl
> > for memdevs that are not CXL_DEVTYPE_CLASSMEM, and return empty strings
> > from memdev attributes associated with data retrieved via the
> > class-device-standard IDENTIFY command. Note that empty strings were
> > chosen over attribute visibility to maintain compatibility with shipping
> > versions of cxl-cli that expect those attributes to always be present.
> > Once cxl-cli has dropped that requirement this workaround can be
> > deprecated.
> > 
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>  
> 
> Reviewed-by: Dave Jiang <dave.jiang@intel.com>

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>