Re: [PATCH 4/5] cxl: Set type of region to that of the first endpoint

[Alejandro Lucero Palau <alucerop@amd.com>]

On 10/17/24 23:33, Dan Williams wrote:
> Huang Ying wrote:
>> Current kernel hard-codes the type of region to type 3 expander now,
>> because this is the only supported device type.  As a preparation to
>> support type 2 accelerators, the patch sets the type of region to that
>> of the first endpoint.  Then, the patch checks whether the type of
>> region is same as the type of other endpoints of the region.  Because
>> what we really need is to make sure the type of all endpoints of a
>> region is same.  And, the patch lets expander/accelerator device
>> drivers specify the target type of endpoint devices via struct
>> cxl_dev_state.
>>
>> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
>> Reviewed-by: Gregory Price <gourry@gourry.net>
>> Cc: Dan Williams <dan.j.williams@intel.com>
>> Cc: Davidlohr Bueso <dave@stgolabs.net>
>> Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
>> Cc: Dave Jiang <dave.jiang@intel.com>
>> Cc: Alison Schofield <alison.schofield@intel.com>
>> Cc: Vishal Verma <vishal.l.verma@intel.com>
>> Cc: Ira Weiny <ira.weiny@intel.com>
>> Cc: Alejandro Lucero <alucerop@amd.com>
>> Cc: Ben Cheatham <benjamin.cheatham@amd.com>
>> ---
>>   drivers/cxl/acpi.c        |  1 -
>>   drivers/cxl/core/hdm.c    | 28 +++++++++++++---------------
>>   drivers/cxl/core/port.c   |  2 ++
>>   drivers/cxl/core/region.c | 13 +++++++------
>>   drivers/cxl/cxl.h         |  1 +
>>   5 files changed, 23 insertions(+), 22 deletions(-)
>>
>> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
>> index 21486e471305..29c2a44b122c 100644
>> --- a/drivers/cxl/acpi.c
>> +++ b/drivers/cxl/acpi.c
>> @@ -382,7 +382,6 @@ static int __cxl_parse_cfmws(struct acpi_cedt_cfmws *cfmws,
>>   
>>   	cxld = &cxlrd->cxlsd.cxld;
>>   	cxld->flags = cfmws_to_decoder_flags(cfmws->restrictions);
>> -	cxld->target_type = CXL_DECODER_EXPANDER;
>>   	cxld->hpa_range = (struct range) {
>>   		.start = cfmws->base_hpa,
>>   		.end = cfmws->base_hpa + cfmws->window_size - 1,
>> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
>> index 478fb6691759..c9accf8be71f 100644
>> --- a/drivers/cxl/core/hdm.c
>> +++ b/drivers/cxl/core/hdm.c
>> @@ -841,18 +841,25 @@ static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
>>   		.end = base + size - 1,
>>   	};
>>   
>> +	if (cxled) {
>> +		struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
>> +		struct cxl_dev_state *cxlds = cxlmd->cxlds;
>> +
>> +		if (cxlds->type == CXL_DEVTYPE_CLASSMEM)
>> +			cxld->target_type = CXL_DECODER_EXPANDER;
>> +		else
>> +			cxld->target_type = CXL_DECODER_ACCEL;
> This looks broken there is no way to know the target type of the decoder
> from the cxl_dev_state. An "accelerator" can have HDM and an "expander"
> can have HDM-DB.
>
>> +	}
>> +
>>   	/* decoders are enabled if committed */
>>   	if (committed) {
>>   		cxld->flags |= CXL_DECODER_F_ENABLE;
>>   		if (ctrl & CXL_HDM_DECODER0_CTRL_LOCK)
>>   			cxld->flags |= CXL_DECODER_F_LOCK;
>> -		if (FIELD_GET(CXL_HDM_DECODER0_CTRL_HOSTONLY, ctrl)) {
>> -			cxld->target_type = CXL_DECODER_EXPANDER;
>> +		if (FIELD_GET(CXL_HDM_DECODER0_CTRL_HOSTONLY, ctrl))
>>   			cxld->coherence = CXL_DECODER_HOSTONLYCOH;
>> -		} else {
>> -			cxld->target_type = CXL_DECODER_ACCEL;
>> +		else
>>   			cxld->coherence = CXL_DECODER_DEVCOH;
>> -		}
>>   
>>   		guard(rwsem_write)(&cxl_region_rwsem);
>>   		if (cxld->id != cxl_num_decoders_committed(port)) {
>> @@ -874,21 +881,12 @@ static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
>>   			struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
>>   			struct cxl_dev_state *cxlds = cxlmd->cxlds;
>>   
>> -			/*
>> -			 * Default by devtype until a device arrives that needs
>> -			 * more precision.
>> -			 */
>> -			if (cxlds->type == CXL_DEVTYPE_CLASSMEM)
>> -				cxld->target_type = CXL_DECODER_EXPANDER;
>> -			else
>> -				cxld->target_type = CXL_DECODER_ACCEL;
>>   			if (cxlds->coherence == CXL_DEVCOH_HOSTONLY)
>>   				cxld->coherence = CXL_DECODER_HOSTONLYCOH;
>>   			else
>>   				cxld->coherence = CXL_DECODER_DEVCOH;
>>   		} else {
>> -			/* To be overridden by region type/coherence at commit time */
>> -			cxld->target_type = CXL_DECODER_EXPANDER;
>> +			/* To be overridden by region coherence at commit time */
>>   			cxld->coherence = CXL_DECODER_HOSTONLYCOH;
>>   		}
>>   
>> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
>> index 9ebbffcea26a..d1bc6aed6509 100644
>> --- a/drivers/cxl/core/port.c
>> +++ b/drivers/cxl/core/port.c
>> @@ -139,6 +139,8 @@ static ssize_t target_type_show(struct device *dev,
>>   		return sysfs_emit(buf, "accelerator\n");
>>   	case CXL_DECODER_EXPANDER:
>>   		return sysfs_emit(buf, "expander\n");
>> +	default:
>> +		break;
>>   	}
>>   	return -ENXIO;
>>   }
>> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
>> index 21b877d8582f..d709738ada61 100644
>> --- a/drivers/cxl/core/region.c
>> +++ b/drivers/cxl/core/region.c
>> @@ -1926,7 +1926,10 @@ static int cxl_region_attach(struct cxl_region *cxlr,
>>   		return -ENXIO;
>>   	}
>>   
>> -	if (cxled->cxld.target_type != cxlr->type) {
>> +	/* Set the type of region to that of the first endpoint */
>> +	if (cxlr->type == CXL_DECODER_INVALID) {
>> +		cxlr->type = cxled->cxld.target_type;
>> +	} else if (cxled->cxld.target_type != cxlr->type) {
> No, the type of the region is determined by the caller and should be
> gated by the region capability. For type-2 region creation I doubt
> userspace is going to be creating those vs the accelerator so this all
> seems backwards to me.


FWIW, path 19 of last type support patchset does add the type to be set 
at region creation time by the caller:

https://lore.kernel.org/linux-cxl/4ce8cc04-71fd-424a-9831-86f89fcd7d2f@amd.com/T/#m420ea86f7b9193519e3226c377612ad3ea546633