linux-kernel - Re: [PATCH v5 5/7] dax: Introduce dax_cxl

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Message-ID: <f9504858-55ca-497f-90f7-ecb20c3027e1@intel.com>
Date: Fri, 23 Jan 2026 15:30:48 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>,
 linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
 nvdimm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
 linux-pm@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>,
 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>,
 Yazen Ghannam <yazen.ghannam@....com>, Davidlohr Bueso <dave@...olabs.net>,
 Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
 "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown <len.brown@...el.com>,
 Pavel Machek <pavel@...nel.org>, Li Ming <ming.li@...omail.com>,
 Jeff Johnson <jeff.johnson@....qualcomm.com>,
 Ying Huang <huang.ying.caritas@...il.com>,
 Yao Xingtao <yaoxt.fnst@...itsu.com>, Peter Zijlstra <peterz@...radead.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Nathan Fontenot <nathan.fontenot@....com>,
 Terry Bowman <terry.bowman@....com>, Robert Richter <rrichter@....com>,
 Benjamin Cheatham <benjamin.cheatham@....com>,
 Zhijian Li <lizhijian@...itsu.com>, Borislav Petkov <bp@...en8.de>,
 Tomasz Wolski <tomasz.wolski@...itsu.com>
Subject: Re: [PATCH v5 5/7] dax: Introduce dax_cxl_mode for CXL coordination

On 1/21/26 9:55 PM, Smita Koralahalli wrote:
> Introduce dax_cxl_mode to coordinate between dax_cxl and dax_hmem when
> handling CXL tagged memory ranges.
> 
> This patch defines the dax_cxl_mode enum and establishes a default policy.
> Subsequent patches will wire this into dax_cxl and dax_hmem to decide
> whether CXL tagged memory ranges should be deferred, registered or
> dropped.

Maybe give some more descriptions of what each enum means?

Maybe just fold this into the patch that first utilizes this enum?

> 
> No functional changes.
> 
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
> ---
>  drivers/dax/bus.c | 3 +++
>  drivers/dax/bus.h | 8 ++++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index fde29e0ad68b..72bc5b76f061 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -24,6 +24,9 @@ DECLARE_RWSEM(dax_region_rwsem);
>   */
>  DECLARE_RWSEM(dax_dev_rwsem);
>  
> +enum dax_cxl_mode dax_cxl_mode = DAX_CXL_MODE_DEFER;
> +EXPORT_SYMBOL_GPL(dax_cxl_mode);

Should this symbol only be exported to CXL?

> +
>  #define DAX_NAME_LEN 30
>  struct dax_id {
>  	struct list_head list;
> diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h
> index cbbf64443098..a40cbbf1e26b 100644
> --- a/drivers/dax/bus.h
> +++ b/drivers/dax/bus.h
> @@ -41,6 +41,14 @@ struct dax_device_driver {
>  	void (*remove)(struct dev_dax *dev);
>  };
>  
> +enum dax_cxl_mode {
> +	DAX_CXL_MODE_DEFER,
> +	DAX_CXL_MODE_REGISTER,
> +	DAX_CXL_MODE_DROP,
> +};
> +
> +extern enum dax_cxl_mode dax_cxl_mode;
> +
>  int __dax_driver_register(struct dax_device_driver *dax_drv,
>  		struct module *module, const char *mod_name);
>  #define dax_driver_register(driver) \