linux-kernel - Re: [PATCH v2 3/5] cxl/acpi: Add platform flag for HPA address translation

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Message-ID: <669086821f136_5fffa29473@dwillia2-xfh.jf.intel.com.notmuch>
Date: Thu, 11 Jul 2024 18:27:30 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Robert Richter <rrichter@....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>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Robert
 Richter" <rrichter@....com>
Subject: Re: [PATCH v2 3/5] cxl/acpi: Add platform flag for HPA address
 translation

Robert Richter wrote:
> Adding an early check to detect platform specifics to (later) enable
> HPA address translation. The cxl_root structure is used to store that
> information.
> 
> Note: The platform check will be added later when enabling address
> translation.

It feels odd to have a flag at the root for this because the translation
is at the host-bridge level, right?

I was more thinking of a solution that does:

spa = cxld_hpa_to_spa(cxld);

...and then internal to that the code walks the port hierarchy from it's
host port to the host bridge. Then does something like

hb->hpa_to_spa(hb, hpa)

Where @hb is:

struct cxl_hb {
	struct cxl_port port;
	u64 (*hpa_to_spa)(struct cxl_hb *, u64);
}