linux-kernel - Re: [PATCH 02/26] cxl/core: Separate region mode from decoder mode

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Date: Mon, 25 Mar 2024 16:20:10 +0000
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: <ira.weiny@...el.com>
CC: Dave Jiang <dave.jiang@...el.com>, Fan Ni <fan.ni@...sung.com>, "Navneet
 Singh" <navneet.singh@...el.com>, Dan Williams <dan.j.williams@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>, Alison Schofield
	<alison.schofield@...el.com>, Vishal Verma <vishal.l.verma@...el.com>,
	<linux-btrfs@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/26] cxl/core: Separate region mode from decoder mode

On Sun, 24 Mar 2024 16:18:05 -0700
ira.weiny@...el.com wrote:

> From: Navneet Singh <navneet.singh@...el.com>
> 
> Until now region modes and decoder modes were equivalent in that they
> were either PMEM or RAM.  With the upcoming addition of Dynamic Capacity
> regions (which will represent an array of device regions [better named
> partitions] the index of which could be different on different
> interleaved devices), the mode of an endpoint decoder and a region will
> no longer be equivalent.
> 
> Define a new region mode enumeration and adjust the code for it.
> 
> Suggested-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Signed-off-by: Navneet Singh <navneet.singh@...el.com>
> Co-developed-by: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>

I can't really remember the reasoning behind this split, but from a fresh
read it seems reasonable. Some trivial comments inline.

Jonathan

> 
> ---
> Changes for v1
> <none>
> ---
>  drivers/cxl/core/region.c | 77 +++++++++++++++++++++++++++++++++++------------
>  drivers/cxl/cxl.h         | 26 ++++++++++++++--
>  2 files changed, 81 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 4c7fd2d5cccb..1723d17f121e 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c


> @@ -2800,6 +2814,24 @@ static int match_region_by_range(struct device *dev, void *data)
>  	return rc;
>  }
>  
> +static enum cxl_region_mode
> +cxl_decoder_to_region_mode(enum cxl_decoder_mode mode)
> +{
> +	switch (mode) {
> +	case CXL_DECODER_NONE:
> +		return CXL_REGION_NONE;
> +	case CXL_DECODER_RAM:
> +		return CXL_REGION_RAM;
> +	case CXL_DECODER_PMEM:
> +		return CXL_REGION_PMEM;
> +	case CXL_DECODER_MIXED:
> +	default:
> +		return CXL_REGION_MIXED;
> +	}
> +

Dead code.

> +	return CXL_REGION_MIXED;
> +}
> +
>  /* Establish an empty region covering the given HPA range */
>  static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
>  					   struct cxl_endpoint_decoder *cxled)
> @@ -2808,12 +2840,17 @@ static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
>  	struct cxl_port *port = cxlrd_to_port(cxlrd);
>  	struct range *hpa = &cxled->cxld.hpa_range;
>  	struct cxl_region_params *p;
> +	enum cxl_region_mode mode;
>  	struct cxl_region *cxlr;
>  	struct resource *res;
>  	int rc;
>  
> +	if (cxled->mode == CXL_DECODER_DEAD)
> +		return ERR_PTR(-EINVAL);

Not a bad thing necessarily, but why do we now need this and didn't before?

> +
> +	mode = cxl_decoder_to_region_mode(cxled->mode);
>  	do {
> -		cxlr = __create_region(cxlrd, cxled->mode,
> +		cxlr = __create_region(cxlrd, mode,
>  				       atomic_read(&cxlrd->region_id));
>  	} while (IS_ERR(cxlr) && PTR_ERR(cxlr) == -EBUSY);


> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 003feebab79b..9a0cce1e6fca 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h


>  /*
>   * Track whether this decoder is reserved for region autodiscovery, or
>   * free for userspace provisioning.
> @@ -511,7 +532,8 @@ struct cxl_region_params {
>   * struct cxl_region - CXL region
>   * @dev: This region's device
>   * @id: This region's id. Id is globally unique across all regions
> - * @mode: Endpoint decoder allocation / access mode
> + * @mode: Region mode which defines which endpoint decoder mode the region is
mode or potentially modes?

If region is mixed, I guess that means endpoint could be pmem or ram in theory?
Don't think anyone has implemented anything yet, but is the potential there?


> + *        compatible with