Re: [PATCH v24 10/11] cxl: Avoid dax creation for accelerators

Alejandro Lucero Palau
2026-03-30T14:27:03Z

On 3/25/26 02:59, Alison Schofield wrote:
> On Mon, Mar 23, 2026 at 11:31:16AM +0000, alejandro.lucero-palau@amd.com wrote:
>> From: Alejandro Lucero <alucerop@amd.com>
>>
>> By definition a type2 cxl device will use the host managed memory for
>> specific functionality, therefore it should not be available to other
>> uses.
> Hi Alejandro,
>
> I'm wondering if we're skipping too much, or perhaps just needs
> a clarifying comment?
>
> Commit message says 'Avoid dax creation...', that's specific.
>
> Commit log says 'should not be available to other uses', that's less specific

Hi Allison,

Would you prefer something like "should not be available to other uses
like DAX".?

> follow me ...
>
>> Signed-off-by: Alejandro Lucero <alucerop@amd.com>
>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>> Reviewed-by: Davidlohr Bueso <daves@stgolabs.net>
>> Reviewed-by: Dave Jiang <dave.jiang@intel.com>
>> Reviewed-by: Ben Cheatham <benjamin.cheatham@amd.com>
>> ---
>> drivers/cxl/core/region.c | 7 +++++++
>> 1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
>> index 8bb53a095290..2f9bdb4f1f4f 100644
>> --- a/drivers/cxl/core/region.c
>> +++ b/drivers/cxl/core/region.c
>> @@ -4263,6 +4263,13 @@ static int cxl_region_probe(struct device *dev)
>> if (rc)
>> return rc;
>>
>> + /*
>> + * HDM-D[B] (device-memory) regions have accelerator specific usage.
>> + * Skip device-dax registration.
>> + */
>> + if (cxlr->type == CXL_DECODER_DEVMEM)
>> + return 0;
>> +
> And above says 'Skip device-dax' specific again, and is indeed skipped.
>
> This escape is not surgically placed at the point where dax is added.
> We are skipping a few other things before dax registration actually
> happens. Why skip memory notifiers, shutdown_notifiers, poison setup?

posion setup crashes with a type2 and I'm not sure if the memory
notifiers make sense for Type2.

If it is really needed, I would prefer to support it as a follow up.

Thank you

>
>> /*
>> * From this point on any path that changes the region's state away from
>> * CXL_CONFIG_COMMIT is also responsible for releasing the driver.
>> --
>> 2.34.1
>>
>>