linux-kernel - Re: [PATCH v1 09/29] cxl/region: Use iterator to find the root port in cxl_find_root

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Message-ID: <Z31jDnsvCSh7DRAf@gourry-fedora-PF4VCD3F>
Date: Tue, 7 Jan 2025 12:23:26 -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 09/29] cxl/region: Use iterator to find the root port
 in cxl_find_root_decoder()

On Tue, Jan 07, 2025 at 03:09:55PM +0100, Robert Richter wrote:
> The function cxl_find_root_decoder() uses find_cxl_root() to find the
> root port. For the implementation of support of address translation an
> iterator is needed that traverses all ports from the endpoint to the
> root port.
> 
> Use the iterator in find_cxl_root() and unfold it into
> cxl_find_root_decoder().
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> ---
>  drivers/cxl/core/region.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 

I wonder if we can expose this mapping in the sysfs hierarchy, because
I've always been frustrated about how confusing what decoders/endpoints
relate to each other.

(I say this not looking forward in the series to see if you did exactly
this, just spitballing)

Reviewed-by: Gregory Price <gourry@...rry.net>

> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 5132c689b1f2..5750ed2796a8 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3206,13 +3206,18 @@ static struct cxl_root_decoder *
>  cxl_find_root_decoder(struct cxl_endpoint_decoder *cxled)
>  {
>  	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> -	struct cxl_port *port = cxled_to_port(cxled);
> -	struct cxl_root *cxl_root __free(put_cxl_root) = find_cxl_root(port);
> +	struct cxl_port *iter = cxled_to_port(cxled);
>  	struct range *hpa = &cxled->cxld.hpa_range;
>  	struct cxl_decoder *cxld = &cxled->cxld;
>  	struct device *cxlrd_dev;
>  
> -	cxlrd_dev = device_find_child(&cxl_root->port.dev, hpa,
> +	while (iter && !is_cxl_root(iter))
> +		iter = to_cxl_port(iter->dev.parent);
> +
> +	if (!iter)
> +		return NULL;
> +
> +	cxlrd_dev = device_find_child(&iter->dev, hpa,
>  				      match_root_decoder_by_range);
>  	if (!cxlrd_dev) {
>  		dev_err(cxlmd->dev.parent,
> -- 
> 2.39.5
>