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: <3a125d7f-7139-4a97-a38c-dfb79c138007@intel.com>
Date: Mon, 15 Sep 2025 09:32:35 -0700
From: Dave Jiang <dave.jiang@...el.com>
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>,
 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 9/15/25 12:55 AM, Robert Richter wrote:
> 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?

All I can say is naming is hard. But cxl_to_hpa_fn() doesn't exactly convey what it does, and we need something that provides a clearer intent preferably. Maybe someone else can have a better suggestion. 

DJ

> 
> -Robert
> 
>>
>> DJ