linux-kernel - Re: [PATCH v1 19/29] cxl/region: Use endpoint's HPA range to find the port's decoder

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Message-ID: <b8aee5a6-6209-4091-962a-dc27253e918a@amd.com>
Date: Fri, 17 Jan 2025 15:31:51 -0600
From: Ben Cheatham <benjamin.cheatham@....com>
To: Robert Richter <rrichter@....com>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Gregory Price
	<gourry@...rry.net>, "Fabio M. De Francesco"
	<fabio.m.de.francesco@...ux.intel.com>, Terry Bowman <terry.bowman@....com>,
	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>
Subject: Re: [PATCH v1 19/29] cxl/region: Use endpoint's HPA range to find the
 port's decoder

On 1/7/25 8:10 AM, Robert Richter wrote:
> For the implementation of address translation it might not be possible
> to determine the root decoder in the early enumeration state since the
> SPA range is still unknown. Instead, the endpoint's HPA range is known
> and from there the topology can be traversed up to the root port while
> the memory range is adjusted from one memory domain to the next up to
> the root port.
> 
> In a first step, use endpoint's HPA range to find the port's decoder.
> Without address translation there is HPA == SPA. Then, the HPA range
> of the endpoint can be used instead of the root decoder's range as
> both are the same.

I think this can be clearer. Something like:

"In a first step, use endpoint's HPA range to find the port's decoder.
Without address translation HPA == SPA, so the endpoint's HPA range can
be used since it is the same as the root decoder's.

> 
> Signed-off-by: Robert Richter <rrichter@....com>
> ---
>  drivers/cxl/core/region.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index b7f6d8a83e4e..23b86de3d4e7 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -861,9 +861,8 @@ static int cxl_port_calc_hpa(struct cxl_port *port, struct cxl_decoder *cxld,
>  
>  static int match_auto_decoder(struct device *dev, void *data)
>  {
> -	struct cxl_region_params *p = data;
> +	struct range *r, *hpa = data;
>  	struct cxl_decoder *cxld;
> -	struct range *r;
>  
>  	if (!is_switch_decoder(dev))
>  		return 0;
> @@ -871,7 +870,7 @@ static int match_auto_decoder(struct device *dev, void *data)
>  	cxld = to_cxl_decoder(dev);
>  	r = &cxld->hpa_range;
>  
> -	if (p->res && p->res->start == r->start && p->res->end == r->end)
> +	if (hpa && hpa->start == r->start && hpa->end == r->end)
>  		return 1;
>  
>  	return 0;
> @@ -888,7 +887,7 @@ cxl_find_decoder_early(struct cxl_port *port,
>  		return &cxled->cxld;
>  
>  	if (test_bit(CXL_REGION_F_AUTO, &cxlr->flags))
> -		dev = device_find_child(&port->dev, &cxlr->params,
> +		dev = device_find_child(&port->dev, &cxled->cxld.hpa_range,
>  					match_auto_decoder);
>  	else
>  		dev = device_find_child(&port->dev, NULL, match_free_decoder);