Re: [PATCH v4 08/26] cxl: add functions for resource request/release by a driver

[Alejandro Lucero Palau <alucerop@amd.com>]

On 10/17/24 22:49, Ben Cheatham wrote:
> On 10/17/24 11:52 AM, alejandro.lucero-palau@amd.com wrote:
>> From: Alejandro Lucero <alucerop@amd.com>
>>
>> Create accessors for an accel driver requesting and releasing a resource.
>>
>> Signed-off-by: Alejandro Lucero <alucerop@amd.com>
>> ---
>>   drivers/cxl/core/memdev.c | 51 +++++++++++++++++++++++++++++++++++++++
>>   include/linux/cxl/cxl.h   |  2 ++
>>   2 files changed, 53 insertions(+)
>>
>> diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
>> index 94b8a7b53c92..4b2641f20128 100644
>> --- a/drivers/cxl/core/memdev.c
>> +++ b/drivers/cxl/core/memdev.c
>> @@ -744,6 +744,57 @@ int cxl_set_resource(struct cxl_dev_state *cxlds, struct resource res,
>>   }
>>   EXPORT_SYMBOL_NS_GPL(cxl_set_resource, CXL);
>>   
>> +int cxl_request_resource(struct cxl_dev_state *cxlds, enum cxl_resource type)
>> +{
>> +	int rc;
>> +
>> +	switch (type) {
>> +	case CXL_RES_RAM:
>> +		if (!resource_size(&cxlds->ram_res)) {
>> +			dev_err(cxlds->dev,
>> +				"resource request for ram with size 0\n");
>> +			return -EINVAL;
>> +		}
>> +
>> +		rc = request_resource(&cxlds->dpa_res, &cxlds->ram_res);
>> +		break;
>> +	case CXL_RES_PMEM:
>> +		if (!resource_size(&cxlds->pmem_res)) {
>> +			dev_err(cxlds->dev,
>> +				"resource request for pmem with size 0\n");
>> +			return -EINVAL;
>> +		}
>> +		rc = request_resource(&cxlds->dpa_res, &cxlds->pmem_res);
>> +		break;
>> +	default:
>> +		dev_err(cxlds->dev, "unsupported resource type (%u)\n", type);
>> +		return -EINVAL;
>> +	}
>> +
>> +	return rc;
>> +}
>> +EXPORT_SYMBOL_NS_GPL(cxl_request_resource, CXL);
> It looks like add_dpa_res() in cxl/core/mbox.c already does what you are doing here, minus the enum.
> Is there a way that could be reused, or a good reason not too? Even if you don't export the function
> outside of the cxl tree, you could reuse that function for the internals of this one.


Although they are obviously similar, I think it makes sense to keep 
both. The CXL accel API is being implemented for avoiding accel drivers 
to manipulate cxl structs but through the API calls. With add_dpa_res we 
would break that, and calling it from the new cxl_request_resource would 
need changes as inside add_dpa_res the resource is initialized what has 
already been done in this implementation. IMO, those changes would make 
the code uglier.


Moreover, your comment below about cxl_dpa_release is, I think, wrong, 
since inside that function other things are being done related to 
regions. BTW, I can not see other release_resource calls from the 
current code than those added by this patch.


So, , I'm not keen to change this now, but maybe a good follow-up work.


>> +
>> +int cxl_release_resource(struct cxl_dev_state *cxlds, enum cxl_resource type)
>> +{
>> +	int rc;
>> +
>> +	switch (type) {
>> +	case CXL_RES_RAM:
>> +		rc = release_resource(&cxlds->ram_res);
>> +		break;
>> +	case CXL_RES_PMEM:
>> +		rc = release_resource(&cxlds->pmem_res);
>> +		break;
>> +	default:
>> +		dev_err(cxlds->dev, "unknown resource type (%u)\n", type);
>> +		return -EINVAL;
>> +	}
>> +
>> +	return rc;
>> +}
>> +EXPORT_SYMBOL_NS_GPL(cxl_release_resource, CXL);
>> +
> Same thing here, but with cxl_dpa_release() instead of add_dpa_res().
>
> Looking at it some more, it looks like there is also some stuff to do with locking for CXL DPA resources in
> that function that you would be skipping with your functions above. Will that be a problem later? I have no
> clue, but thought I should ask just in case.
>
>>   static int cxl_memdev_release_file(struct inode *inode, struct file *file)
>>   {
>>   	struct cxl_memdev *cxlmd =
>> diff --git a/include/linux/cxl/cxl.h b/include/linux/cxl/cxl.h
>> index 2f48ee591259..6c6d27721067 100644
>> --- a/include/linux/cxl/cxl.h
>> +++ b/include/linux/cxl/cxl.h
>> @@ -54,4 +54,6 @@ bool cxl_pci_check_caps(struct cxl_dev_state *cxlds,
>>   			unsigned long *expected_caps,
>>   			unsigned long *current_caps);
>>   int cxl_pci_accel_setup_regs(struct pci_dev *pdev, struct cxl_dev_state *cxlds);
>> +int cxl_request_resource(struct cxl_dev_state *cxlds, enum cxl_resource type);
>> +int cxl_release_resource(struct cxl_dev_state *cxlds, enum cxl_resource type);
>>   #endif