linux-kernel - Re: [PATCH v1 10/29] cxl/region: Add function to find a port's switch decoder by range

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Message-ID: <Z310qYmGmGqqhY53@gourry-fedora-PF4VCD3F>
Date: Tue, 7 Jan 2025 13:38:33 -0500
From: Gregory Price <gourry@...rry.net>
To: Robert Richter <rrichter@....com>
Cc: Alison Schofield <alison.schofield@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Ira Weiny <ira.weiny@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>, linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>,
	Terry Bowman <terry.bowman@....com>
Subject: Re: [PATCH v1 10/29] cxl/region: Add function to find a port's
 switch decoder by range

On Tue, Jan 07, 2025 at 03:09:56PM +0100, Robert Richter wrote:
> Factor out code to find the switch decoder of a port for a specific
> address range. Reuse the code to search a root decoder, create the
> function cxl_port_find_switch_decoder() and rework
> match_root_decoder_by_range() to be usable for switch decoders too.
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> ---
>  drivers/cxl/core/region.c | 43 +++++++++++++++++++++++----------------
>  1 file changed, 25 insertions(+), 18 deletions(-)
... snip ...
>  
> -	cxlrd_dev = device_find_child(&iter->dev, hpa,
> -				      match_root_decoder_by_range);
> -	if (!cxlrd_dev) {
> +	cxld = cxl_port_find_switch_decoder(iter, hpa);
> +	if (!cxld) {

Are there scenarios where this would return a different decoder than
previously? For example, is there an assumption that root decoders
will be search first, as opposed to intermediate decoders?

The match function was changed to check is_switch_decoder from
is_root_decoder, i'm just worried about the case where we might have
multiple decoders in the path and the switch decoder is hit first -
resulting in the wrong decoder returned.

~Gregory