linux-kernel - Re: [PATCH v3 11/18] cxl/region: Split region registration into an initialization and adding part

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Message-ID: <20250214162407.00002efc@huawei.com>
Date: Fri, 14 Feb 2025 16:24:07 +0000
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Robert Richter <rrichter@....com>
CC: Alison Schofield <alison.schofield@...el.com>, Vishal Verma
	<vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, Dan Williams
	<dan.j.williams@...el.com>, Dave Jiang <dave.jiang@...el.com>, "Davidlohr
 Bueso" <dave@...olabs.net>, <linux-cxl@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Gregory Price <gourry@...rry.net>, "Fabio M.
 De Francesco" <fabio.m.de.francesco@...ux.intel.com>, Terry Bowman
	<terry.bowman@....com>
Subject: Re: [PATCH v3 11/18] cxl/region: Split region registration into an
 initialization and adding part

On Tue, 11 Feb 2025 10:53:41 +0100
Robert Richter <rrichter@....com> wrote:

> Before adding an endpoint to a region, the endpoint is initialized
> first. Move that part to a new function
> cxl_endpoint_decoder_initialize(). The function is in preparation of
> adding more parameters that need to be determined in a setup.
> 
> The split also helps better separating the code. After initialization
> the addition of an endpoint may fail with an error code and all the
> data would need to be reverted to not leave the endpoint in an
> undefined state. With separate functions the init part can succeed
> even if the endpoint cannot be added.
> 
> Function naming follows the style of device_register() etc. Thus,
> rename function cxl_add_to_region() to
> cxl_endpoint_decoder_register().
Hi Robert,

Superficially I'd expect a call of that name to be registering
the device for the decoder.  i.e. being the thing that makes
/sys/bus/cxl/devices/decoder3.2 appear.

This register naming is based on the other two being initalize
and add, but they aren't initializing and adding the
endpoint decode device. Hence I don't think those names work either.

> 
> Signed-off-by: Robert Richter <rrichter@....com>
> Reviewed-by: Gregory Price <gourry@...rry.net>
> Tested-by: Gregory Price <gourry@...rry.net>
> ---
>  drivers/cxl/core/region.c | 36 ++++++++++++++++++++++++++++--------
>  drivers/cxl/cxl.h         |  6 ++++--
>  drivers/cxl/port.c        |  9 +++++----
>  3 files changed, 37 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 9ce0282c0042..fb43e154c7b9 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3345,7 +3345,7 @@ static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
>  		dev_name(&cxlr->dev), p->res, p->interleave_ways,
>  		p->interleave_granularity);
>  
> -	/* ...to match put_device() in cxl_add_to_region() */
> +	/* ...to match put_device() in cxl_endpoint_decoder_add() */
>  	get_device(&cxlr->dev);
>  	up_write(&cxl_region_rwsem);
>  
> @@ -3357,19 +3357,28 @@ static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
>  	return ERR_PTR(rc);
>  }
>  
> -int cxl_add_to_region(struct cxl_endpoint_decoder *cxled)
> +static int cxl_endpoint_decoder_initialize(struct cxl_endpoint_decoder *cxled)
So far this looks like it should be called something like

cxl_endpoint_decoder_init_region_decoder()
or something like that. The cxled is already intialized more generally
and the cxled->cxld.dev is registered.

>  {
> -	struct range *hpa = &cxled->cxld.hpa_range;
>  	struct cxl_root_decoder *cxlrd;
> -	struct cxl_region_params *p;
> -	struct cxl_region *cxlr;
> -	bool attach = false;
> -	int rc;
>  
>  	cxlrd = cxl_find_root_decoder(cxled);
>  	if (!cxlrd)
>  		return -ENXIO;
>  
> +	cxled->cxlrd = cxlrd;
> +
> +	return 0;
> +}
> +
> +static int cxl_endpoint_decoder_add(struct cxl_endpoint_decoder *cxled)
It's not adding what I'd expect such a function to add.
Rather it is performing an association with a region.

> +{
> +	struct range *hpa = &cxled->cxld.hpa_range;
> +	struct cxl_root_decoder *cxlrd = cxled->cxlrd;
> +	struct cxl_region_params *p;
> +	struct cxl_region *cxlr;
> +	bool attach = false;
> +	int rc;
> +
>  	/*
>  	 * Ensure that if multiple threads race to construct_region() for @hpa
>  	 * one does the construction and the others add to that.
> @@ -3406,7 +3415,18 @@ int cxl_add_to_region(struct cxl_endpoint_decoder *cxled)
>  
>  	return rc;
>  }
> -EXPORT_SYMBOL_NS_GPL(cxl_add_to_region, "CXL");
> +
> +int cxl_endpoint_decoder_register(struct cxl_endpoint_decoder *cxled)
> +{
> +	int rc;
> +
> +	rc = cxl_endpoint_decoder_initialize(cxled);
> +	if (rc)
> +		return rc;
> +
> +	return cxl_endpoint_decoder_add(cxled);
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_endpoint_decoder_register, "CXL");