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

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Message-ID: <20250415145016.00003725@huawei.com>
Date: Tue, 15 Apr 2025 14:50:16 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: <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>, Alejandro Lucero <alucerop@....com>
Subject: Re: [PATCH v13 11/22] cxl: define a driver interface for HPA free
 space enumeration

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?

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