netdev - Re: [PATCH v14 11/22] cxl: define a driver interface for HPA free space enumeration

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Message-ID: <683ab376-62f8-449b-8db3-5179854d7cd7@amd.com>
Date: Mon, 28 Apr 2025 09:00:51 +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 v14 11/22] cxl: define a driver interface for HPA free
 space enumeration


On 4/22/25 17:22, Jonathan Cameron wrote:
> On Thu, 17 Apr 2025 22:29:14 +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>
>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>> +	/*
>> +	 * None flags are declared as bitmaps but for the sake of better code
>> +	 * used here as such, restricting the bitmap size to those bits used by
>> +	 * any Type2 device driver requester.
> I'd just drop the comment as it's more confusing than helpful.
>
> If you really want something then perhaps.
>
> 	* Flags are single unsigned longs. As CXL_DECODER_F_MAX is less than
> 	* 32 bits the bitmap functions may be used.


As I said in v13, I just want to make sure none reading this code, and 
realizing those flags are not defined as bitmaps, being confused.


I can use your suggestion. I'll wait for more reviews for a potential 
v15 ... I guess/hope I have not been the only one off this last week ...


Thanks


>> +	 */
>> +	if (!bitmap_subset(&ctx->flags, &cxld->flags, CXL_DECODER_F_MAX)) {
>> +		dev_dbg(dev, "flags not matching: %08lx vs %08lx\n",
>> +			cxld->flags, ctx->flags);
>> +		return 0;
>> +	}
>