netdev - Re: [PATCH v10 14/26] cxl: define a driver interface for HPA free space enumeration

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Message-ID: <b34f139e-6fe3-4a4b-8090-1abe3788ecba@amd.com>
Date: Mon, 17 Feb 2025 13:49:10 +0000
From: Alejandro Lucero Palau <alucerop@....com>
To: Alison Schofield <alison.schofield@...el.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 v10 14/26] cxl: define a driver interface for HPA free
 space enumeration


On 2/13/25 04:08, Alison Schofield wrote:
> On Wed, Feb 05, 2025 at 03:19:38PM +0000, alucerop@....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>
>> Co-developed-by: Dan Williams <dan.j.williams@...el.com>
> Checkpatch WARNS on more than one of these in the set.
> Dan's SOB goes after his Co-dev tag.


I've commented about this in other patchset versions. I think Dan 
co-developed makes sense since it is based on his original patchset 
dealing with initial type2 support, but it does not seem right to me 
adding a SOB.

If this is a problem, I will just comment about the original work and 
remove the co-developed line.


>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>> ---
>>   drivers/cxl/core/region.c | 160 ++++++++++++++++++++++++++++++++++++++
>>   drivers/cxl/cxl.h         |   3 +
>>   include/cxl/cxl.h         |  10 +++
>>   3 files changed, 173 insertions(+)
>>
>> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
>> index 84ce625b8591..69ff00154298 100644
>> --- a/drivers/cxl/core/region.c
>> +++ b/drivers/cxl/core/region.c
>> @@ -695,6 +695,166 @@ static int free_hpa(struct cxl_region *cxlr)
>>   	return 0;
>>   }
>>   
>> +struct cxlrd_max_context {
>> +	struct device * const *host_bridges;
>> +	int interleave_ways;
>> +	unsigned long flags;
>> +	resource_size_t max_hpa;
>> +	struct cxl_root_decoder *cxlrd;
>> +};
>> +
>> +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;
>> +
>> +	if (!is_root_decoder(dev))
>> +		return 0;
>> +
>> +	cxlrd = to_cxl_root_decoder(dev);
>> +	cxlsd = &cxlrd->cxlsd;
>> +	cxld = &cxlsd->cxld;
>> +	if ((cxld->flags & ctx->flags) != ctx->flags) {
>> +		dev_dbg(dev, "flags not matching: %08lx vs %08lx\n",
>> +			cxld->flags, ctx->flags);
>> +		return 0;
>> +	}
>> +
>> +	for (int i = 0; i < ctx->interleave_ways; i++)
>> +		for (int j = 0; j < ctx->interleave_ways; j++)
>> +			if (ctx->host_bridges[i] == cxlsd->target[j]->dport_dev) {
>> +				found++;
>> +				break;
>> +			}
>> +
> Above deserves another bracket at least on the outer for loop:
> https://www.kernel.org/doc/html/latest/process/coding-style.html
> "Also, use braces when a loop contains more than a single simple
> statement"


I'll do.


>
>> +	if (found != ctx->interleave_ways) {
> Adding on to Simons feedback: Even if found is OK as 0, prefer it be
> initialized so we don't have to think about it on every static report.
>

OK. I'll do.

Thanks