netdev - Re: [PATCH v11 18/23] cxl: allow region creation by type2 drivers

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Message-ID: <311bcb0d-0ba2-46d0-acc3-87c119cd9e54@amd.com>
Date: Wed, 12 Mar 2025 08:28:53 +0000
From: Alejandro Lucero Palau <alucerop@....com>
To: Ben Cheatham <benjamin.cheatham@....com>, alejandro.lucero-palau@....com
Cc: linux-cxl@...r.kernel.org, netdev@...r.kernel.org,
 dan.j.williams@...el.com, edward.cree@....com, davem@...emloft.net,
 kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com, dave.jiang@...el.com
Subject: Re: [PATCH v11 18/23] cxl: allow region creation by type2 drivers


On 3/11/25 20:06, Ben Cheatham wrote:
> On 3/10/25 4:03 PM, alejandro.lucero-palau@....com wrote:
>> From: Alejandro Lucero <alucerop@....com>
>>
>> Creating a CXL region requires userspace intervention through the cxl
>> sysfs files. Type2 support should allow accelerator drivers to create
>> such cxl region from kernel code.
>>
>> Adding that functionality and integrating it with current support for
>> memory expanders.
>>
>> Based on https://lore.kernel.org/linux-cxl/168592159835.1948938.1647215579839222774.stgit@dwillia2-xfh.jf.intel.com/
>>
>> Signed-off-by: Alejandro Lucero <alucerop@....com>
>> ---
>>   drivers/cxl/core/region.c | 133 +++++++++++++++++++++++++++++++++++---
>>   drivers/cxl/port.c        |   5 +-
>>   include/cxl/cxl.h         |   4 ++
>>   3 files changed, 133 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
>> index e24666a419cd..e6fbe00d0623 100644
>> --- a/drivers/cxl/core/region.c
>> +++ b/drivers/cxl/core/region.c
>> @@ -2310,6 +2310,17 @@ static int cxl_region_detach(struct cxl_endpoint_decoder *cxled)
>>   	return rc;
>>   }
>>   
>> +int cxl_accel_region_detach(struct cxl_endpoint_decoder *cxled)
>> +{
>> +	int rc;
>> +
>> +	guard(rwsem_write)(&cxl_region_rwsem);
>> +	cxled->part = -1;
>> +	rc = cxl_region_detach(cxled);
>> +	return rc;
>> +}
>> +EXPORT_SYMBOL_NS_GPL(cxl_accel_region_detach, "CXL");
>> +
>>   void cxl_decoder_kill_region(struct cxl_endpoint_decoder *cxled)
>>   {
>>   	down_write(&cxl_region_rwsem);
>> @@ -2816,6 +2827,14 @@ cxl_find_region_by_name(struct cxl_root_decoder *cxlrd, const char *name)
>>   	return to_cxl_region(region_dev);
>>   }
>>   
>> +static void drop_region(struct cxl_region *cxlr)
>> +{
>> +	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
>> +	struct cxl_port *port = cxlrd_to_port(cxlrd);
>> +
>> +	devm_release_action(port->uport_dev, unregister_region, cxlr);
>> +}
>> +
> Nit: There are a couple of spots in this file that call the above devm_release_action,
> I think it would be good to replace those with a call to this function. You
> could also get rid of drop_region() and use devm_release_action() instead.


I'll take a look.


>>   static ssize_t delete_region_store(struct device *dev,
>>   				   struct device_attribute *attr,
>>   				   const char *buf, size_t len)
> [snip]
>
>> +/**
>> + * cxl_create_region - Establish a region given an endpoint decoder
>> + * @cxlrd: root decoder to allocate HPA
>> + * @cxled: endpoint decoder with reserved DPA capacity
>> + *
>> + * Returns a fully formed region in the commit state and attached to the
>> + * cxl_region driver.
>> + */
>> +struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
>> +				     struct cxl_endpoint_decoder *cxled, int ways)
> Sorry if I'm behind the times, but is it no longer a requirement for accelerator drivers
> to have interleaving disabled (i.e. interleave_ways = 1)?


It is unlikely but there is no restriction by the specs and Dan 
suggested supporting this situation was not complicated, so better to do 
it from the start.