linux-kernel - Re: [PATCH v1 04/29] cxl/pci: Add comments to cxl_hdm_decode

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Message-ID: <Z31bizrgbgjj-RXG@gourry-fedora-PF4VCD3F>
Date: Tue, 7 Jan 2025 11:51:23 -0500
From: Gregory Price <gourry@...rry.net>
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>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>, linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>,
	Terry Bowman <terry.bowman@....com>
Subject: Re: [PATCH v1 04/29] cxl/pci: Add comments to cxl_hdm_decode_init()

On Tue, Jan 07, 2025 at 03:09:50PM +0100, Robert Richter 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>
> ---
>  drivers/cxl/core/pci.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 

This addresses some of my prior questions, but I still think this
function is worth some extra scrutiny.

Reviewed-by: Gregory Price <gourry@...rry.net>

> diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> index c7050c13f71a..4d2154457efb 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.
>  	 */
>  	if (!info->mem_enabled) {
>  		rc = devm_cxl_enable_hdm(&port->dev, cxlhdm);
> -- 
> 2.39.5
>