linux-kernel - Re: [PATCH v3 04/18] cxl/pci: Add comments to cxl_hdm_decode

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Message-ID: <20250214155120.00004461@huawei.com>
Date: Fri, 14 Feb 2025 15:51:20 +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 04/18] cxl/pci: Add comments to cxl_hdm_decode_init()

On Tue, 11 Feb 2025 10:53:34 +0100
Robert Richter <rrichter@....com> wrote:

> There are various configuration cases of HDM decoder registers causing
> different code paths. Add comments to cxl_hdm_decode_init() to better
> explain them.
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> Reviewed-by: Gregory Price <gourry@...rry.net>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Tested-by: Gregory Price <gourry@...rry.net>
> ---
>  drivers/cxl/core/pci.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> index c49efc419285..6333a01e4f19 100644
> --- a/drivers/cxl/core/pci.c
> +++ b/drivers/cxl/core/pci.c
> @@ -416,9 +416,17 @@ int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm,
>  	if (global_ctrl & CXL_HDM_DECODER_ENABLE || (!hdm && info->mem_enabled))
>  		return devm_cxl_enable_mem(&port->dev, cxlds);
>  
> +	/*
> +	 * If the HDM Decoder Capability does not exist and DVSEC was
> +	 * not setup, the DVSEC based emulation cannot be used.
> +	 */
>  	if (!hdm)
>  		return -ENODEV;
>  
> +	/*
> +	 * The HDM Decoder Capability exists but is globally disabled.
> +	 */
> +
>  	/*
>  	 * Per CXL 2.0 Section 8.1.3.8.3 and 8.1.3.8.4 DVSEC CXL Range 1 Base
>  	 * [High,Low] when HDM operation is enabled the range register values
> @@ -426,7 +434,8 @@ int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm,
>  	 * DVSEC Range 1,2 to HDM Decoder Range 0,1. So, non-zero info->ranges
>  	 * are expected even though Linux does not require or maintain that
>  	 * match. If at least one DVSEC range is enabled and allowed, skip HDM
> -	 * Decoder Capability Enable.
> +	 * Decoder Capability Enable. Else, use the HDM Decoder Capability and
> +	 * enable it.

As per previous.  Having an 'else' comment that refers to what happens if the
following if is true, just adds to confusion :(

So if you are going to move the comment it needs a more substantial rewrite
to reflect that we care 'here' about that last bit only.

>  	 */
>  	if (!info->mem_enabled) {
>  		rc = devm_cxl_enable_hdm(&port->dev, cxlhdm);