Re: [PATCH v9 17/27] cxl: define a driver interface for DPA allocation

Alejandro Lucero Palau
2025-01-03T07:58:23Z

On 1/2/25 15:15, Jonathan Cameron wrote:
> On Mon, 30 Dec 2024 21:44:35 +0000
> <alejandro.lucero-palau@amd.com> wrote:
>
>> From: Alejandro Lucero <alucerop@amd.com>
>>
>> Region creation involves finding available DPA (device-physical-address)
>> capacity to map into HPA (host-physical-address) space. Given the HPA
>> capacity constraint, define an API, cxl_request_dpa(), that has the
>> flexibility to map the minimum amount of memory the driver needs to
>> operate vs the total possible that can be mapped given HPA availability.
>>
>> Factor out the core of cxl_dpa_alloc, that does free space scanning,
>> into a cxl_dpa_freespace() helper, and use that to balance the capacity
>> available to map vs the @min and @max arguments to cxl_request_dpa.
>>
>> Based on https://lore.kernel.org/linux-cxl/168592158743.1948938.7622563891193802610.stgit@dwillia2-xfh.jf.intel.com/
>>
>> Signed-off-by: Alejandro Lucero <alucerop@amd.com>
>> Co-developed-by: Dan Williams <dan.j.williams@intel.com>
> A couple of really minor things inline. Either way
>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>
>> +/**
>> + * cxl_request_dpa - search and reserve DPA given input constraints
>> + * @cxlmd: memdev with an endpoint port with available decoders
>> + * @is_ram: DPA operation mode (ram vs pmem)
>> + * @min: the minimum amount of capacity the call needs
>> + * @max: HPA capacity available
>> + *
>> + * Given that a region needs to allocate from limited HPA capacity it
>> + * may be the case that a device has more mappable DPA capacity than
>> + * available HPA. So, the expectation is that @min is a driver known
>> + * value for how much capacity is needed, and @max is based the limit of
> is the limit? Not sure what the "is based" means

Typo from original Dan's patches.

I'll fix it.

>
>> + * how much HPA space is available for a new region.
>> + *
>> + * Returns a pinned cxl_decoder with at least @min bytes of capacity
>> + * reserved, or an error pointer. The caller is also expected to own the
>> + * lifetime of the memdev registration associated with the endpoint to
>> + * pin the decoder registered as well.
>> + */
>> +struct cxl_endpoint_decoder *cxl_request_dpa(struct cxl_memdev *cxlmd,
>> + bool is_ram,
>> + resource_size_t min,
>> + resource_size_t max)
>> +{
>> + struct cxl_port *endpoint = cxlmd->endpoint;
>> + struct cxl_endpoint_decoder *cxled;
>> + enum cxl_decoder_mode mode;
>> + struct device *cxled_dev;
>> + resource_size_t alloc;
>> + int rc;
>> +
>> + if (!IS_ALIGNED(min | max, SZ_256M))
>> + return ERR_PTR(-EINVAL);
>> +
>> + down_read(&cxl_dpa_rwsem);
>> + cxled_dev = device_find_child(&endpoint->dev, NULL, find_free_decoder);
>> + up_read(&cxl_dpa_rwsem);
>> +
>> + if (!cxled_dev)
>> + return ERR_PTR(-ENXIO);
>> +
>> + cxled = to_cxl_endpoint_decoder(cxled_dev);
>> +
>> + if (!cxled) {
>> + put_device(cxled_dev);
>> + return ERR_PTR(-ENODEV);
> Ah. My suggestion on v8 missed that there is an error block
> below. More consistent with rest of the code as
>
> rc = -ENODEV;
> goto err;
>

I'll do.

Thanks!

>> + }
>> +
>> + if (is_ram)
>> + mode = CXL_DECODER_RAM;
>> + else
>> + mode = CXL_DECODER_PMEM;
>> +
>> + rc = cxl_dpa_set_mode(cxled, mode);
>> + if (rc)
>> + goto err;
>> +
>> + down_read(&cxl_dpa_rwsem);
>> + alloc = cxl_dpa_freespace(cxled, NULL, NULL);
>> + up_read(&cxl_dpa_rwsem);
>> +
>> + if (max)
>> + alloc = min(max, alloc);
>> + if (alloc < min) {
>> + rc = -ENOMEM;
>> + goto err;
>> + }
>> +
>> + rc = cxl_dpa_alloc(cxled, alloc);
>> + if (rc)
>> + goto err;
>> +
>> + return cxled;
>> +err:
>> + put_device(cxled_dev);
>> + return ERR_PTR(rc);
>> +}
>> +EXPORT_SYMBOL_NS_GPL(cxl_request_dpa, "CXL");
>