Re: [PATCH v7 8/8] cxl: Allow auto-committed BI hdm decoders

On Tue, 04 Aug 2026, Alison Schofield wrote:

>On Tue, Jul 28, 2026 at 07:41:36AM -0700, Davidlohr Bueso wrote:
>> @@ -1061,13 +1061,23 @@ static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
>>		else
>>			cxld->target_type = CXL_DECODER_DEVMEM;
>>
>> -		/*
>> -		 * Autocommit BI-enabled decoders is not supported.
>> -		 * At this point cxlds->bi is not yet setup, so there
>> -		 * are no guarantees that the platform supports BI.
>> -		 */
>> -		if (FIELD_GET(CXL_HDM_DECODER0_CTRL_BI, ctrl))
>> -			return -ENXIO;
>> +		if (FIELD_GET(CXL_HDM_DECODER0_CTRL_BI, ctrl)) {
>> +			struct cxl_dev_state *cxlds = cxled ?
>> +				cxled_to_memdev(cxled)->cxlds : NULL;
>
>Here we first read CTRL register -
>
>> +
>> +			if (cxld->target_type == CXL_DECODER_HOSTONLYMEM) {
>> +				dev_warn(&port->dev,
>> +					 "decoder%d.%d: BI with host-only\n",
>> +					 port->id, cxld->id);
>> +				return -ENXIO;
>> +			}
>> +			if (cxlds && !cxlds->bi_capable) {
>> +				dev_warn(&port->dev,
>> +					 "decoder%d.%d: path not BI capable\n",
>> +					 port->id, cxld->id);
>> +				return -ENXIO;
>> +			}
>> +		}
>>
>>		guard(rwsem_write)(&cxl_rwsem.region);
>>		if (cxld->id != cxl_num_decoders_committed(port)) {
>>
>> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
>> index 76c6dc28a407..5578ef68034d 100644
>> --- a/drivers/cxl/core/region.c
>> +++ b/drivers/cxl/core/region.c
>> @@ -1827,6 +1827,21 @@ static int cxl_region_attach_position(struct cxl_region *cxlr,
>>	return rc;
>>  }
>>
⇞>> +/* Read back the committed BI bit of an auto-discovered decoder */
>> +static bool cxled_committed_bi(struct cxl_endpoint_decoder *cxled)
>> +{
>> +	struct cxl_port *port = cxled_to_port(cxled);
>> +	struct cxl_hdm *cxlhdm = dev_get_drvdata(&port->dev);
>> +	u32 ctrl;
>> +
>> +	if (!cxlhdm || !cxlhdm->regs.hdm_decoder)
>> +		return false;
>> +
>> +	ctrl = readl(cxlhdm->regs.hdm_decoder +
>> +		     CXL_HDM_DECODER0_CTRL_OFFSET(cxled->cxld.id));
>> +	return FIELD_GET(CXL_HDM_DECODER0_CTRL_BI, ctrl);
>
>And then we re-read it here.  Could we record the bit at the earlier read?

I prefer not adding complexity in managing a new flag (ie: now we have to deal
with symmetry for the manual region creation counterpart, syncing etc.) at
the cost of one readl per decoder as regions are assembled.

Thanks,
Davidlohr

>
>
>> +}
>
>snip to end