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Message-ID: <2ec3e22c-ca17-03e0-aff2-15d7ccea2ab0@amd.com>
Date: Fri, 27 Dec 2024 08:46:01 +0000
From: Alejandro Lucero Palau <alucerop@....com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
alejandro.lucero-palau@....com
Cc: linux-cxl@...r.kernel.org, netdev@...r.kernel.org,
dan.j.williams@...el.com, martin.habets@...inx.com, edward.cree@....com,
davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
edumazet@...gle.com, dave.jiang@...el.com
Subject: Re: [PATCH v8 23/27] cxl: add region flag for precluding a device
memory to be used for dax
On 12/24/24 18:04, Jonathan Cameron wrote:
> On Mon, 16 Dec 2024 16:10:38 +0000
> <alejandro.lucero-palau@....com> wrote:
>
>> From: Alejandro Lucero <alucerop@....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. However, a dax interface could be just good enough in some cases.
>>
>> Add a flag to a cxl region for specifically state to not create a dax
>> device. Allow a Type2 driver to set that flag at region creation time.
> So this is presented as something a type 2 driver would chose to set
> or not. That feels premature if for now they are all going to set
> it?
I would say, by definition, a type2 should avoid dax, but it could be
dax just what is needed.
I was told to add this option in previous reviews, and I considered it
more flexible and harmless.
>> Signed-off-by: Alejandro Lucero <alucerop@....com>
>> Reviewed-by: Zhi Wang <zhiw@...dia.com>
>> ---
>> drivers/cxl/core/region.c | 11 ++++++++++-
>> drivers/cxl/cxl.h | 3 +++
>> drivers/cxl/cxlmem.h | 3 ++-
>> include/cxl/cxl.h | 3 ++-
>> 4 files changed, 17 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
>> index a24d8678e8dc..aeaa6868e556 100644
>> --- a/drivers/cxl/core/region.c
>> +++ b/drivers/cxl/core/region.c
>> @@ -3557,12 +3557,14 @@ __construct_new_region(struct cxl_root_decoder *cxlrd,
>> * cxl_create_region - Establish a region given an endpoint decoder
>> * @cxlrd: root decoder to allocate HPA
>> * @cxled: endpoint decoder with reserved DPA capacity
>> + * @no_dax: if true no DAX device should be created
>> *
>> * 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)
>> + struct cxl_endpoint_decoder *cxled,
>> + bool no_dax)
>> {
>> struct cxl_region *cxlr;
>>
>> @@ -3578,6 +3580,10 @@ struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
>> drop_region(cxlr);
>> return ERR_PTR(-ENODEV);
>> }
>> +
>> + if (no_dax)
>> + set_bit(CXL_REGION_F_NO_DAX, &cxlr->flags);
>> +
>> return cxlr;
>> }
>> EXPORT_SYMBOL_NS_GPL(cxl_create_region, "CXL");
>> @@ -3713,6 +3719,9 @@ static int cxl_region_probe(struct device *dev)
>> if (rc)
>> return rc;
>>
>> + if (test_bit(CXL_REGION_F_NO_DAX, &cxlr->flags))
>> + return 0;
>> +
>> switch (cxlr->mode) {
>> case CXL_DECODER_PMEM:
>> return devm_cxl_add_pmem_region(cxlr);
>> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
>> index 57d6dda3fb4a..cc9e3d859fa6 100644
>> --- a/drivers/cxl/cxl.h
>> +++ b/drivers/cxl/cxl.h
>> @@ -521,6 +521,9 @@ struct cxl_region_params {
>> */
>> #define CXL_REGION_F_NEEDS_RESET 1
>>
>> +/* Allow Type2 drivers to specify if a dax region should not be created. */
>> +#define CXL_REGION_F_NO_DAX 2
>> +
>> /**
>> * struct cxl_region - CXL region
>> * @dev: This region's device
>> diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
>> index 9d874f1cb3bf..712f25f494e0 100644
>> --- a/drivers/cxl/cxlmem.h
>> +++ b/drivers/cxl/cxlmem.h
>> @@ -875,5 +875,6 @@ struct seq_file;
>> struct dentry *cxl_debugfs_create_dir(const char *dir);
>> void cxl_dpa_debug(struct seq_file *file, struct cxl_dev_state *cxlds);
>> struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
>> - struct cxl_endpoint_decoder *cxled);
>> + struct cxl_endpoint_decoder *cxled,
>> + bool no_dax);
>> #endif /* __CXL_MEM_H__ */
>> diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
>> index e0ea5b801a2e..14be26358f9c 100644
>> --- a/include/cxl/cxl.h
>> +++ b/include/cxl/cxl.h
>> @@ -61,7 +61,8 @@ struct cxl_endpoint_decoder *cxl_request_dpa(struct cxl_memdev *cxlmd,
>> resource_size_t max);
>> int cxl_dpa_free(struct cxl_endpoint_decoder *cxled);
>> struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
>> - struct cxl_endpoint_decoder *cxled);
>> + struct cxl_endpoint_decoder *cxled,
>> + bool no_dax);
>>
>> int cxl_accel_region_detach(struct cxl_endpoint_decoder *cxled);
>> #endif
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