Re: [PATCH 3/4] acpi: numa: Add setting of generic port system locality attributes

[Dave Jiang <dave.jiang@intel.com>]

On 5/12/23 9:16 AM, Jonathan Cameron wrote:
> On Fri, 05 May 2023 17:05:28 -0700
> Dave Jiang <dave.jiang@intel.com> wrote:
> 
>> Add generic port support for the parsing of HMAT system locality sub-table.
>> The attributes will be added to the third array member of the access
>> coordinates in order to not mix with the existing memory attributes it only
>> provides the system locality attributes from initator to the generic port
>> targets and is missing the rest of the data to the actual memory device.
>>
>> The complete attributes will be updated when a memory device is
>> attached and the system locality information is calculated end to end.
>>
>> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> 
> Strange question for you.  For now we have it easy as we only have Type 3
> CXL devices using this.  Later when we have accelerators, then the generic
> port becomes both an initiator and a target (well proxy of one in both cases).
> We'll probably want to map the linux view of a generic initiator (CPU less
> node) on top of the accelerator using the access characteristics from HMAT +
> other parts.
> 
> Any thoughts on how to extend this approach to that case?

I have not given much thought on it. But I'll think on it.

> 
> I can see it might need another access class so that normal memory for example
> can be the target of a generic port.
> 
> Maybe it's worth predicting that and renaming CLASS_GENPORT to CLASS_GENPORT_SINK
> or something along those lines?

Sure. We can name it to something more specific with an eye on the 
future. But we can deal with the rest when the time comes.

> 
> Or just leave it until someone cares?  I'm fine with this answer if you agree ;)
> 
> Jonathan
> 
>> ---
>>   drivers/acpi/numa/hmat.c |    7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
>> index e2ab1cce0add..951579e903cf 100644
>> --- a/drivers/acpi/numa/hmat.c
>> +++ b/drivers/acpi/numa/hmat.c
>> @@ -60,6 +60,7 @@ struct target_cache {
>>   enum {
>>   	NODE_ACCESS_CLASS_0 = 0,
>>   	NODE_ACCESS_CLASS_1,
>> +	NODE_ACCESS_CLASS_GENPORT,
>>   	NODE_ACCESS_CLASS_MAX,
>>   };
>>   
>> @@ -368,6 +369,12 @@ static __init int hmat_parse_locality(union acpi_subtable_headers *header,
>>   			if (mem_hier == ACPI_HMAT_MEMORY) {
>>   				target = find_mem_target(targs[targ]);
>>   				if (target && target->processor_pxm == inits[init]) {
>> +					if (*target->device_handle) {
>> +						hmat_update_target_access(target, type, value,
>> +								NODE_ACCESS_CLASS_GENPORT);
>> +						continue;
>> +					}
>> +
>>   					hmat_update_target_access(target, type, value,
>>   								  NODE_ACCESS_CLASS_0);
>>   					/* If the node has a CPU, update access 1 */
>>
>>
>