netdev - Re: [PATCH v13 11/22] cxl: define a driver interface for HPA free space enumeration

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Message-ID: <eb5f16f8-607a-4c71-8f81-5cdb4ff73a75@amd.com>
Date: Thu, 17 Apr 2025 13:11:00 +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, edward.cree@....com, davem@...emloft.net,
 kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com, dave.jiang@...el.com
Subject: Re: [PATCH v13 11/22] cxl: define a driver interface for HPA free
 space enumeration


On 4/15/25 14:50, Jonathan Cameron wrote:
> On Mon, 14 Apr 2025 16:13:25 +0100
> alejandro.lucero-palau@....com wrote:
>
>> From: Alejandro Lucero <alucerop@....com>
>>
>> CXL region creation involves allocating capacity from device DPA
>> (device-physical-address space) and assigning it to decode a given HPA
>> (host-physical-address space). Before determining how much DPA to
>> allocate the amount of available HPA must be determined. Also, not all
>> HPA is created equal, some specifically targets RAM, some target PMEM,
>> some is prepared for device-memory flows like HDM-D and HDM-DB, and some
>> is host-only (HDM-H).
>>
>> Wrap all of those concerns into an API that retrieves a root decoder
>> (platform CXL window) that fits the specified constraints and the
>> capacity available for a new region.
>>
>> Add a complementary function for releasing the reference to such root
>> decoder.
>>
>> Based on https://lore.kernel.org/linux-cxl/168592159290.1948938.13522227102445462976.stgit@dwillia2-xfh.jf.intel.com/
>>
>> Signed-off-by: Alejandro Lucero <alucerop@....com>
> One trivial comment inline.
>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>
>> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
>> index 80caaf14d08a..0a9eab4f8e2e 100644
>> --- a/drivers/cxl/core/region.c
>> +++ b/drivers/cxl/core/region.c
>> +static int find_max_hpa(struct device *dev, void *data)
>> +{
>> +	struct cxlrd_max_context *ctx = data;
>> +	struct cxl_switch_decoder *cxlsd;
>> +	struct cxl_root_decoder *cxlrd;
>> +	struct resource *res, *prev;
>> +	struct cxl_decoder *cxld;
>> +	resource_size_t max;
>> +	int found = 0;
>> +
>> +	if (!is_root_decoder(dev))
>> +		return 0;
>> +
>> +	cxlrd = to_cxl_root_decoder(dev);
>> +	cxlsd = &cxlrd->cxlsd;
>> +	cxld = &cxlsd->cxld;
>> +
>> +	/*
>> +	 * None flags are declared as bitmaps but for the sake of better code
> None?


Not sure you refer to syntax or semantics here. Assuming is the former:


No flags fields?


>
>> +	 * used here as such, restricting the bitmap size to those bits used by
>> +	 * any Type2 device driver requester.
>> +	 */
>