linux-kernel - Re: [PATCH v3 07/11] cxl: Introduce callback to translate a decoder's HPA to the next parent port

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Message-ID: <aMfGgKqVp1Ue0eQa@rric.localdomain>
Date: Mon, 15 Sep 2025 09:55:44 +0200
From: Robert Richter <rrichter@....com>
To: Dave Jiang <dave.jiang@...el.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>,
	Davidlohr Bueso <dave@...olabs.net>, 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>,
	Joshua Hahn <joshua.hahnjy@...il.com>
Subject: Re: [PATCH v3 07/11] cxl: Introduce callback to translate a
 decoder's HPA to the next parent port

On 12.09.25 14:21:16, Dave Jiang wrote:
> 
> 
> On 9/12/25 7:45 AM, Robert Richter wrote:
> > To enable address translation, the endpoint decoder's HPA range must
> > be translated when crossing memory domains to the next parent port's
> > address ranges up to the root port. The root port's HPA range is
> > equivalent to the system's SPA range.
> > 
> > Introduce a callback to translate an address of the decoder's HPA
> > range to the address range of the parent port. The callback can be set
> > for ports that need to handle address translation.
> > 
> > Reviewed-by: Gregory Price <gourry@...rry.net>
> > Signed-off-by: Robert Richter <rrichter@....com>
> > ---
> >  drivers/cxl/cxl.h | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> > index f182982f1c14..eb837867d932 100644
> > --- a/drivers/cxl/cxl.h
> > +++ b/drivers/cxl/cxl.h
> > @@ -429,6 +429,17 @@ struct cxl_rd_ops {
> >  	u64 (*spa_to_hpa)(struct cxl_root_decoder *cxlrd, u64 spa);
> >  };
> >  
> > +/**
> > + * cxl_to_hpa_fn - type of a callback function to translate an HPA
> > + * @cxld: cxl_decoder to translate from
> > + * @hpa: HPA of the @cxld decoder's address range
> > + *
> > + * The callback translates a decoder's HPA to the address range of the
> > + * decoder's parent port. The return value is the translated HPA on
> > + * success or ULLONG_MAX otherwise.
> > + */
> > +typedef u64 (*cxl_to_hpa_fn)(struct cxl_decoder *cxld, u64 hpa);
> 
> cxl_to_parent_hpa_fn()?

It is actually a translation from the decoder's address space to the
address space of the port this callback is attached to. Parent port
might be confusing here and maybe the comment needs a rework too.
Though, finally it is used in the context where the decoder's port is
child to the port with this callback.

Comment should be more precise, ok?

-Robert

> 
> DJ