linux-kernel - Re: [PATCH v4 11/14] cxl/atl: Lock decoders that need address translation

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Message-ID: <6f1eaf10-071c-41ad-bda3-62eb6b1119e9@intel.com>
Date: Wed, 12 Nov 2025 09:34:34 -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 v4 11/14] cxl/atl: Lock decoders that need address
 translation

On 11/11/25 5:54 AM, Robert Richter wrote:
> On 04.11.25 10:13:34, Dave Jiang wrote:
>>
>>
>> On 11/3/25 11:47 AM, Robert Richter wrote:
>>> There is only support to translate addresses from an endpoint to its
>>> CXL host bridge, but not in the opposite direction from the bridge to
>>> the endpoint. Thus, the endpoint address range cannot be determined
>>> and setup manually for a given SPA range of a region. If the endpoint
>>> has address translation enabled, lock it to prevent the kernel from
>>> reconfiguring it.
>>>
>>> Reviewed-by: Gregory Price <gourry@...rry.net>
>>> Signed-off-by: Robert Richter <rrichter@....com>
>>> ---
>>>  drivers/cxl/core/atl.c | 10 ++++++++++
>>>  1 file changed, 10 insertions(+)
>>>
>>> diff --git a/drivers/cxl/core/atl.c b/drivers/cxl/core/atl.c
>>> index d6aa7e6d0ac5..5c15e4d12193 100644
>>> --- a/drivers/cxl/core/atl.c
>>> +++ b/drivers/cxl/core/atl.c
>>> @@ -158,6 +158,16 @@ static int cxl_prm_translate_hpa_range(struct cxl_root *cxl_root, void *data)
>>>  		return -ENXIO;
>>>  	}
>>>  
>>> +	/*
>>> +	 * There is only support to translate from the endpoint to its
>>> +	 * parent port, but not in the opposite direction from the
>>> +	 * parent to the endpoint. Thus, the endpoint address range
>>> +	 * cannot be determined and setup manually. If the address range
>>> +	 * was translated and modified, forbid reprogramming of the
>>> +	 * decoders and lock them.
>>> +	 */
>>> +	cxld->flags |= CXL_DECODER_F_LOCK;
>>
>  
>> Feels like this should be something the BIOS should enforce if that
>> is the expectation? And the kernel checks and warns if that is not
>> the case.
> 
> I think this is more a limitation of the kernel implementation rather
> than the BIOS. The BIOS provides enought information by CFMWS, PRM,
> HDM and PCI topology. In theory and if there is demand for it, support
> could be added for driver region setup.

But shouldn't the BIOS set the decoder lock rather than the kernel setting a software lock flag based on assumption of the PRM based setup?

DJ

> 
> -Robert
> 
>>
>>> +
>>>  	ctx->hpa_range = hpa_range;
>>>  	ctx->interleave_ways = ways;
>>>  	ctx->interleave_granularity = gran;
>>
> ?