Re: [PATCH 12/23] cxl: Introduce endpoint decoders

On Mon, Nov 22, 2021 at 11:38 AM Ben Widawsky [off-list ref] wrote:

On 21-11-22 16:20:39, Jonathan Cameron wrote:

quoted

On Fri, 19 Nov 2021 16:02:39 -0800
Ben Widawsky [off-list ref] wrote:

quoted

Endpoints have decoders too. It is useful to share the same
infrastructure from cxl_core. Endpoints do not have dports (downstream
targets), only the underlying physical medium. As a result, some special
casing is needed.

There is no functional change introduced yet as endpoints don't actually
enumerate decoders yet.

Signed-off-by: Ben Widawsky <redacted>

I'm not a fan of special values like using 0 here to indicate endpoint
device.  I'd rather see a base cxl_decode_alloc(..., bool ep)
and possibly wrappers for the non ep case and ep one.

Jonathan

My inclination is the opposite. However, I think you and Dan both brought up
something to this effect in the previous RFCs.

Dan, do you have a preference here?

I was thinking something along the lines of what Jonathan wants,
explicit per-type APIs, but internal / private to the core can use
heuristics like nr_targets == 0 == endpoint.

So unexport cxl_decoder_alloc() and have separate:

cxl_root_decoder_alloc()
cxl_switch_decoder_alloc()
cxl_endpoint_decoder_alloc()

...apis that use a static cxl_decoder_alloc() internally. Probably
also wants a cxl_endpoint_decoder_add() that drops the need to pass a
NULL @target_map.