netdev - Re: [PATCH v7 17/28] cxl: define a driver interface for DPA allocation

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Message-ID: <33368384-8ec4-fc3e-9e98-9864632eec6c@amd.com>
Date: Fri, 13 Dec 2024 09:37:35 +0000
From: Alejandro Lucero Palau <alucerop@....com>
To: Simon Horman <horms@...nel.org>, 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 v7 17/28] cxl: define a driver interface for DPA
 allocation


On 12/12/24 18:12, Simon Horman wrote:
> On Mon, Dec 09, 2024 at 06:54:18PM +0000, alejandro.lucero-palau@....com wrote:
>> From: Alejandro Lucero <alucerop@....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@....com>
>> Co-developed-by: Dan Williams <dan.j.williams@...el.com>
>> ---
>>   drivers/cxl/core/hdm.c | 154 +++++++++++++++++++++++++++++++++++------
>>   include/cxl/cxl.h      |   5 ++
>>   2 files changed, 138 insertions(+), 21 deletions(-)
>>
>> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> ...
>
>> @@ -538,6 +557,99 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
>>   	return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
>>   }
>>   
>> +static int find_free_decoder(struct device *dev, void *data)
>> +{
>> +	struct cxl_endpoint_decoder *cxled;
>> +	struct cxl_port *port;
>> +
>> +	if (!is_endpoint_decoder(dev))
>> +		return 0;
>> +
>> +	cxled = to_cxl_endpoint_decoder(dev);
>> +	port = cxled_to_port(cxled);
>> +
>> +	if (cxled->cxld.id != port->hdm_end + 1)
>> +		return 0;
>> +
>> +	return 1;
>> +}
>> +
>> +/**
>> + * cxl_request_dpa - search and reserve DPA given input constraints
>> + * @endpoint: an endpoint port with available decoders
> nit: @cxlmd should be described here rather than @endpoint


Uhmm, confusing ... I saw this reported by the robot in v6, and I had 
updated it ... but obviously I lost the change during the different 
testing stages moving the patchset around.


I will fix it  ... again :-).


Thanks!


>
>> + * @is_ram: DPA operation mode (ram vs pmem)
>> + * @min: the minimum amount of capacity the call needs
>> + * @max: extra capacity to allocate after min is satisfied
>> + *
>> + * 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
>> + * 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)
> ...