linux-kernel - Re: [PATCH v4 05/14] cxl/region: Rename function to cxl_find_decoder

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Message-ID: <67c9fcd7e7fd3_1a7729440@dwillia2-xfh.jf.intel.com.notmuch>
Date: Thu, 6 Mar 2025 11:51:51 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Robert Richter <rrichter@....com>, 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>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>, Dave Jiang
	<dave.jiang@...el.com>, Davidlohr Bueso <dave@...olabs.net>
CC: <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>,
	Robert Richter <rrichter@....com>
Subject: Re: [PATCH v4 05/14] cxl/region: Rename function to
 cxl_find_decoder_early()

Robert Richter wrote:
> Current function cxl_region_find_decoder() is used to find a port's
> decoder during region setup. The decoder is later used to attach the
> port to a region.
> 
> Rename function to cxl_find_decoder_early() to emphasize its use only
> during region setup in the early pre-init setup stage when an endpoint
> is not yet attached to a region (cxl_region_attach()). Once a port is
> attached to a region, the region reference can be used to lookup a
> region's port and decoder configuration (see struct cxl_region_ref).
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> Reviewed-by: Gregory Price <gourry@...rry.net>
> Tested-by: Gregory Price <gourry@...rry.net>

"_early" to me has always meant "before some other subsystem dependency
is available", like the "page allocator not initialized". So I do not
think this name helps readability.

> ---
>  drivers/cxl/core/region.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 4f79cc17c9c8..e40ae0fefddc 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -865,10 +865,18 @@ static int match_auto_decoder(struct device *dev, const void *data)
>  	return 0;
>  }
>  
> +/*
> + * Only use cxl_find_decoder_early() during region setup in the early
> + * pre-init setup stage when an endpoint is not yet attached to a
> + * region (cxl_region_attach()). Once a port is attached to a region,
> + * the region reference can be used to lookup a region's port and
> + * decoder configuration (see struct cxl_region_ref).
> +*/

I like the sentiment that this function is only for setup paths before
the given port has a cxl_region_ref established for the region, but
"pre-init" is not defined. Let's just call this function what it is and
document when to use without making the reader of this comment wonder
what "pre-init" means. Something like:

/**
 * cxl_port_pick_region_decoder() - assign or lookup a decoder for a region
 * @port: a port in the ancestry of the endpoint implied by @cxled
 * @cxled: endpoint decoder to be, or currently, mapped by @port
 * @cxlr: region to establish, or validate, decode @port
 *
 * In the region creation path cxl_port_pick_region_decoder() is an
 * allocator to find a free port. In the region assembly path, it is
 * recalling the decoder that platform firmware picked for validation
 * purposes.
 *
 * The result is recorded in a 'struct cxl_region_ref' in @port for
 * later recall when other endpoints might also be targets of the picked
 * decoder.
 */