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

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Message-ID: <20250417173650.00003ee0@huawei.com>
Date: Thu, 17 Apr 2025 17:36:50 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Alejandro Lucero Palau <alucerop@....com>
CC: <alejandro.lucero-palau@....com>, <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 Thu, 17 Apr 2025 13:11:00 +0100
Alejandro Lucero Palau <alucerop@....com> wrote:

> 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:
Just the wording of the comment. I'm not sure what it means.

> 
> 
> No flags fields?

Not following that either.
> 
> 
> >  
> >> +	 * used here as such, restricting the bitmap size to those bits used by
> >> +	 * any Type2 device driver requester.
> >> +	 */  
> >