linux-kernel - Re: [PATCH v2 03/15] cxl/region: Factor out code for interleaving calculations

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Message-ID: <Z7dYODuRrRv1bXpV@gourry-fedora-PF4VCD3F>
Date: Thu, 20 Feb 2025 11:28:40 -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 v2 03/15] cxl/region: Factor out code for interleaving
 calculations

On Tue, Feb 18, 2025 at 02:23:44PM +0100, Robert Richter wrote:
> Function cxl_calc_interleave_pos() contains code to calculate the
> interleaving parameters of a port. Factor out that code for later
> reuse. Add function cxl_port_calc_interleave() for this and introduce
> struct cxl_interleave_context to collect all interleaving data.
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> ---
>  drivers/cxl/core/region.c | 63 ++++++++++++++++++++++++++-------------
>  1 file changed, 43 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index c118bda93e86..ad4a6ce37216 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -1800,27 +1800,34 @@ static int find_pos_and_ways(struct cxl_port *port, struct range *range,
>  	return rc;
>  }
>  
> +struct cxl_interleave_context {
> +	struct range *hpa_range;
> +	int pos;
> +};
> +

I get that this will be used later to pass information back, but this
patch by itself is a little confusing because ctx seems pointless since
the function still returns the position and accesses the hpa_range directly

Looked at in isolation, having the context structure change in this
patch than just adding the hpa_range as an argument and adding the
context later when it's actually relevant.

static int cxl_port_calc_interleave(struct cxl_port *port,
				    struct range *hpa_range);

> +static int cxl_calc_interleave_pos(struct cxl_endpoint_decoder *cxled)
> +{
> +	struct cxl_port *iter, *port = cxled_to_port(cxled);
> +	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> +	struct cxl_interleave_context ctx;
> +	int pos = 0;
> +
> +	ctx = (struct cxl_interleave_context) {
> +		.hpa_range = &cxled->cxld.hpa_range,
> +	};
> +
> +	for (iter = cxled_to_port(cxled); pos >= 0 && iter;
> +	     iter = parent_port_of(iter))
> +		pos = cxl_port_calc_interleave(iter, &ctx);
>  
>  	dev_dbg(&cxlmd->dev,
>  		"decoder:%s parent:%s port:%s range:%#llx-%#llx pos:%d\n",
>  		dev_name(&cxled->cxld.dev), dev_name(cxlmd->dev.parent),
> -		dev_name(&port->dev), range->start, range->end, pos);
> +		dev_name(&port->dev), ctx.hpa_range->start, ctx.hpa_range->end,
> +		ctx.pos);
> 

	context just gets discarded here and hpa_range and pos are
	otherwise still accessible if you just pass hpa_range as an
	argument.  So I would push off adding the context argument to
	the patch that actually needs it.

>  	return pos;
>  }

~Gregory