linux-kernel - Re: [RFC 3/5] cxl: Separate coherence from target type

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Message-ID: <87plojnxog.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date: Wed, 02 Oct 2024 08:41:35 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Gregory Price <gourry@...rry.net>
Cc: Dan Williams <dan.j.williams@...el.com>,  Dave Jiang
 <dave.jiang@...el.com>,  linux-cxl@...r.kernel.org,
  linux-kernel@...r.kernel.org,  Jonathan Cameron
 <Jonathan.Cameron@...wei.com>,  Davidlohr Bueso <dave@...olabs.net>,
  Alison Schofield <alison.schofield@...el.com>,  Vishal Verma
 <vishal.l.verma@...el.com>,  Ira Weiny <ira.weiny@...el.com>,  Alejandro
 Lucero <alucerop@....com>
Subject: Re: [RFC 3/5] cxl: Separate coherence from target type

Gregory Price <gourry@...rry.net> writes:

> On Wed, Sep 25, 2024 at 10:46:45AM +0800, Huang Ying wrote:
>> Previously, target type (expander or accelerator) and
>> coherence (HOSTONLY (HDM-H) or DEV (HDM-D/DB)) are synonym.  So target
>> type is used to designate coherence too.  However, it's possible for
>> expanders to use HDM-DB now.  So, we need to separate coherence from
>> target type.
>> 
>> Accordingly, the HOSTONLY field of decoder ctrl
>> register (CXL_HDM_DECODER0_CTRL_HOSTONLY) need to be set according to
>> coherence.
>> 
>> The coherence of decoders can not be determined via target type too.
>> So, accelerator/expander device drivers need to specify coherence
>> explicitly via newly added coherence field in struct cxl_dev_state.
>> 
>> The coherence of each end points in a region need to be same.  So, the
>> coherence of the first end point is recorded in struct region.  Which
>> will be checked against the coherence of all other end points.
>> 
>> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
>> Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>> Cc: Dan Williams <dan.j.williams@...el.com>
>> Cc: Davidlohr Bueso <dave@...olabs.net>
>> Cc: Jonathan Cameron <jonathan.cameron@...wei.com>
>> Cc: Dave Jiang <dave.jiang@...el.com>
>> Cc: Alison Schofield <alison.schofield@...el.com>
>> Cc: Vishal Verma <vishal.l.verma@...el.com>
>> Cc: Ira Weiny <ira.weiny@...el.com>
>> Cc: Alejandro Lucero <alucerop@....com>
>> ---
>>  drivers/cxl/core/hdm.c    | 22 +++++++++++++++-------
>>  drivers/cxl/core/mbox.c   |  1 +
>>  drivers/cxl/core/port.c   |  1 +
>>  drivers/cxl/core/region.c | 37 ++++++++++++++++++++++++++++++++++---
>>  drivers/cxl/cxl.h         |  9 +++++++++
>>  drivers/cxl/cxlmem.h      | 11 +++++++++++
>>  6 files changed, 71 insertions(+), 10 deletions(-)
>> 
>
> Reviewed-by: Gregory Price <gourry@...rry.net>

Thanks!

>> @@ -1925,6 +1933,29 @@ static int cxl_region_attach(struct cxl_region *cxlr,
>>  		return -ENXIO;
>>  	}
>>  
>> +	/* Set the coherence of region to that of the first endpoint */
>> +	if (cxlr->coherence == CXL_DECODER_INVALIDCOH) {
>> +		unsigned long flags = cxlrd->cxlsd.cxld.flags;
>> +		enum cxl_decoder_coherence coherence = cxled->cxld.coherence;
>> +
>> +		cxlr->coherence = coherence;
>> +		if ((coherence == CXL_DECODER_HOSTONLYCOH &&
>> +		     !(flags & CXL_DECODER_F_HOSTONLYCOH)) ||
>> +		    (coherence == CXL_DECODER_DEVCOH &&
>> +		     !(flags & CXL_DECODER_F_DEVCOH))) {
>
> silly nit but my gut tells me we can make this less ugly.
> Not a blocker though.

Yes.  This looks urgly.  Will think about how to improve it.

>> +			dev_dbg(&cxlr->dev,
>> +"%s:%s endpoint coherence: %d isn't supported by root decoder: %#lx\n",
>> +				dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
>> +				coherence, flags);
>> +			return -ENXIO;
>> +		}

--
Best Regards,
Huang, Ying