Re: [PATCH v2] Documentation/driver-api/cxl: device hotplug section

[Jonathan Cameron]

On Thu, 18 Dec 2025 12:07:47 -0500
Gregory Price <gourry@xxxxxxxxxx> wrote:

> Describe cxl memory device hotplug implications, in particular how the
> platform CEDT CFMWS must be described to support successful hot-add of
> memory devices.
> 
> Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>
> ---
> v2: Jonathan's clarifications and diagrams.

One request for a reference given I'm not sure the whole multi-endpoint memory
device thing is going to hang around so that might confuse people reading
this in future - particularly as it isn't something the spec mentions.

With something added there (or a statement that there isn't anything public that
will do the job)

Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>

> diff --git a/Documentation/driver-api/cxl/platform/device-hotplug.rst b/Documentation/driver-api/cxl/platform/device-hotplug.rst
> new file mode 100644
> index 000000000000..617e340bd556
> --- /dev/null
> +++ b/Documentation/driver-api/cxl/platform/device-hotplug.rst

> +
> +Multi-Endpoint Memory Device Present at Boot
> +--------------------------------------------
> +A hot-plug capable CXL memory device, such as one which presents multiple
> +expanders as a single large-capacity device, should report the maximum
> +*possible* capacity for the device at boot. ::
> +
> +                  HB0
> +                  RP0
> +                   |
> +     [Multi-Endpoint Memory Device]

So this is the weird switch as end point thing?   Maybe a reference.
My guess is these will go away as switch and memory device vendors catch
up with the spec, but maybe I'm wrong.

> +              _____|_____
> +             |          |
> +        [Endpoint0]   [Empty]
> +
> +
> +Limiting the size to the capacity preset at boot will limit hot-add support
> +to replacing capacity that was present at boot.