netdev - Re: [PATCH v2 09/15] cxl: define a driver interface for HPA free space enumaration

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Message-ID: <446d8183-d334-bf5c-8ba8-de957b7e8edb@amd.com>
Date: Wed, 28 Aug 2024 11:41:11 +0100
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, richard.hughes@....com
Subject: Re: [PATCH v2 09/15] cxl: define a driver interface for HPA free
 space enumaration


On 8/4/24 18:57, Jonathan Cameron wrote:
> + }
>> +	return 0;
>> +}
>> +
>> +/**
>> + * cxl_get_hpa_freespace - find a root decoder with free capacity per constraints
>> + * @endpoint: an endpoint that is mapped by the returned decoder
>> + * @interleave_ways: number of entries in @host_bridges
>> + * @flags: CXL_DECODER_F flags for selecting RAM vs PMEM, and HDM-H vs HDM-D[B]
>> + * @max: output parameter of bytes available in the returned decoder
> @available_size
> or something along those lines. I'd expect max to be the end address of the available
> region


No really. The code looks for the biggest free hole in the HPA. 
Returning available size does not help except from informing about the 
"internal fragmentation".


>> + *
>> + * The return tuple of a 'struct cxl_root_decoder' and 'bytes available (@max)'
>> + * is a point in time snapshot. If by the time the caller goes to use this root
>> + * decoder's capacity the capacity is reduced then caller needs to loop and
>> + * retry.
>> + *
>> + * The returned root decoder has an elevated reference count that needs to be
>> + * put with put_device(cxlrd_dev(cxlrd)). Locking context is with
>> + * cxl_{acquire,release}_endpoint(), that ensures removal of the root decoder
>> + * does not race.
>> + */
>> +struct cxl_root_decoder *cxl_get_hpa_freespace(struct cxl_port *endpoint,
>> +					       int interleave_ways,
>> +					       unsigned long flags,
>> +					       resource_size_t *max)
>> +{
>> +
>> +	struct cxlrd_max_context ctx = {
>> +		.host_bridges = &endpoint->host_bridge,
>> +		.interleave_ways = interleave_ways,
>> +		.flags = flags,
>> +	};
>> +	struct cxl_port *root_port;
>> +	struct cxl_root *root;
>> +
>> +	if (!is_cxl_endpoint(endpoint)) {
>> +		dev_dbg(&endpoint->dev, "hpa requestor is not an endpoint\n");
>> +		return ERR_PTR(-EINVAL);
>> +	}
>> +
>> +	root = find_cxl_root(endpoint);
>> +	if (!root) {
>> +		dev_dbg(&endpoint->dev, "endpoint can not be related to a root port\n");
>> +		return ERR_PTR(-ENXIO);
>> +	}
>> +
>> +	root_port = &root->port;
>> +	down_read(&cxl_region_rwsem);
>> +	device_for_each_child(&root_port->dev, &ctx, find_max_hpa);
>> +	up_read(&cxl_region_rwsem);
>> +	put_device(&root_port->dev);
>> +
>> +	if (!ctx.cxlrd)
>> +		return ERR_PTR(-ENOMEM);
>> +
>> +	*max = ctx.max_hpa;
> Rename max_hpa to available_hpa.
>
>> +	return ctx.cxlrd;
>> +}
>> +EXPORT_SYMBOL_NS_GPL(cxl_get_hpa_freespace, CXL);
>> +
>> +