linux-kernel - Re: [PATCH v4 6/7] dax/hmem: Save the DAX HMEM platform device pointer

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Message-ID: <f4b861fe-d10e-497e-b7d3-af4af9c58cac@intel.com>
Date: Thu, 5 Jun 2025 09:54:06 -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: Davidlohr Bueso <dave@...olabs.net>,
 Jonathan Cameron <jonathan.cameron@...wei.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>, 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 KH <gregkh@...uxfoundation.org>,
 Nathan Fontenot <nathan.fontenot@....com>,
 Terry Bowman <terry.bowman@....com>, Robert Richter <rrichter@....com>,
 Benjamin Cheatham <benjamin.cheatham@....com>,
 PradeepVineshReddy Kodamati <PradeepVineshReddy.Kodamati@....com>,
 Zhijian Li <lizhijian@...itsu.com>
Subject: Re: [PATCH v4 6/7] dax/hmem: Save the DAX HMEM platform device
 pointer



On 6/3/25 3:19 PM, Smita Koralahalli wrote:
> From: Nathan Fontenot <nathan.fontenot@....com>
> 
> To enable registration of HMEM devices for SOFT RESERVED regions after
> the DAX HMEM device is initialized, this patch saves a reference to the
> DAX HMEM platform device.
> 
> This saved pointer will be used in a follow-up patch to allow late
> registration of SOFT RESERVED memory ranges. It also enables
> simplification of the walk_hmem_resources() by removing the need to
> pass a struct device argument.
> 
> There are no functional changes.
> 
> Co-developed-by: Nathan Fontenot <Nathan.Fontenot@....com>
> Signed-off-by: Nathan Fontenot <Nathan.Fontenot@....com>
> Co-developed-by: Terry Bowman <terry.bowman@....com>
> Signed-off-by: Terry Bowman <terry.bowman@....com>
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
> ---
>  drivers/dax/hmem/device.c | 4 ++--
>  drivers/dax/hmem/hmem.c   | 9 ++++++---
>  include/linux/dax.h       | 5 ++---
>  3 files changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/dax/hmem/device.c b/drivers/dax/hmem/device.c
> index f9e1a76a04a9..59ad44761191 100644
> --- a/drivers/dax/hmem/device.c
> +++ b/drivers/dax/hmem/device.c
> @@ -17,14 +17,14 @@ static struct resource hmem_active = {
>  	.flags = IORESOURCE_MEM,
>  };
>  
> -int walk_hmem_resources(struct device *host, walk_hmem_fn fn)
> +int walk_hmem_resources(walk_hmem_fn fn)
>  {
>  	struct resource *res;
>  	int rc = 0;
>  
>  	mutex_lock(&hmem_resource_lock);
>  	for (res = hmem_active.child; res; res = res->sibling) {
> -		rc = fn(host, (int) res->desc, res);
> +		rc = fn((int) res->desc, res);
>  		if (rc)
>  			break;
>  	}
> diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c
> index 5e7c53f18491..3aedef5f1be1 100644
> --- a/drivers/dax/hmem/hmem.c
> +++ b/drivers/dax/hmem/hmem.c
> @@ -9,6 +9,8 @@
>  static bool region_idle;
>  module_param_named(region_idle, region_idle, bool, 0644);
>  
> +static struct platform_device *dax_hmem_pdev;
> +
>  static int dax_hmem_probe(struct platform_device *pdev)
>  {
>  	unsigned long flags = IORESOURCE_DAX_KMEM;
> @@ -59,9 +61,9 @@ static void release_hmem(void *pdev)
>  	platform_device_unregister(pdev);
>  }
>  
> -static int hmem_register_device(struct device *host, int target_nid,
> -				const struct resource *res)
> +static int hmem_register_device(int target_nid, const struct resource *res)
>  {
> +	struct device *host = &dax_hmem_pdev->dev;
>  	struct platform_device *pdev;
>  	struct memregion_info info;
>  	long id;
> @@ -125,7 +127,8 @@ static int hmem_register_device(struct device *host, int target_nid,
>  
>  static int dax_hmem_platform_probe(struct platform_device *pdev)
>  {
> -	return walk_hmem_resources(&pdev->dev, hmem_register_device);
> +	dax_hmem_pdev = pdev;

Is there never more than 1 DAX HMEM platform device that can show up? The global pointer makes me nervous.

DJ

> +	return walk_hmem_resources(hmem_register_device);
>  }
>  
>  static struct platform_driver dax_hmem_platform_driver = {
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index dcc9fcdf14e4..a4ad3708ea35 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -305,7 +305,6 @@ static inline void hmem_register_resource(int target_nid, struct resource *r)
>  }
>  #endif
>  
> -typedef int (*walk_hmem_fn)(struct device *dev, int target_nid,
> -			    const struct resource *res);
> -int walk_hmem_resources(struct device *dev, walk_hmem_fn fn);
> +typedef int (*walk_hmem_fn)(int target_nid, const struct resource *res);
> +int walk_hmem_resources(walk_hmem_fn fn);
>  #endif