linux-kernel - Re: [RFC PATCH 15/20] cxl: Add a routine to find cxl root decoder on cxl bus

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Message-ID: <29487b27-ad1a-4c6d-a1a7-26eb97e77663@intel.com>
Date: Thu, 10 Jul 2025 09:23:59 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: Neeraj Kumar <s.neeraj@...sung.com>, dan.j.williams@...el.com,
 dave@...olabs.net, jonathan.cameron@...wei.com, alison.schofield@...el.com,
 vishal.l.verma@...el.com, ira.weiny@...el.com
Cc: a.manzanares@...sung.com, nifan.cxl@...il.com, anisa.su@...sung.com,
 vishak.g@...sung.com, krish.reddy@...sung.com, arun.george@...sung.com,
 alok.rathore@...sung.com, neeraj.kernel@...il.com,
 linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
 nvdimm@...ts.linux.dev, gost.dev@...sung.com, cpgs@...sung.com
Subject: Re: [RFC PATCH 15/20] cxl: Add a routine to find cxl root decoder on
 cxl bus



On 6/17/25 5:39 AM, Neeraj Kumar wrote:
> Add cxl_find_root_decoder to find root decoder on cxl bus. It is used to
> find root decoder during region creation
> 
> Signed-off-by: Neeraj Kumar <s.neeraj@...sung.com>
> ---
>  drivers/cxl/core/port.c | 26 ++++++++++++++++++++++++++
>  drivers/cxl/cxl.h       |  1 +
>  2 files changed, 27 insertions(+)
> 
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index 2452f7c15b2d..94d9322b8e38 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -513,6 +513,32 @@ struct cxl_switch_decoder *to_cxl_switch_decoder(struct device *dev)
>  }
>  EXPORT_SYMBOL_NS_GPL(to_cxl_switch_decoder, "CXL");
>  
> +static int match_root_decoder(struct device *dev, void *data)
> +{
> +	return is_root_decoder(dev);
> +}
> +
> +/**
> + * cxl_find_root_decoder() - find a cxl root decoder on cxl bus
> + * @port: any descendant port in root-cxl-port topology

s/root-cxl-port/CXL port/

Please add a comment noting that the caller of this function must call put_device() when done as a device ref is taken via device_find_child().

> + */
> +struct cxl_root_decoder *cxl_find_root_decoder(struct cxl_port *port)

cxl_port_find_root_decoder(). There is a cxl_find_root_decoder() already in core/region.c and could cause potential symbol clash.

DJ

> +{
> +	struct cxl_root *cxl_root __free(put_cxl_root) = find_cxl_root(port);
> +	struct device *dev;
> +
> +	if (!cxl_root)
> +		return NULL;
> +
> +	dev = device_find_child(&cxl_root->port.dev, NULL, match_root_decoder);
> +
> +	if (!dev)
> +		return NULL;
> +
> +	return to_cxl_root_decoder(dev);
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_find_root_decoder, "CXL");
> +
>  static void cxl_ep_release(struct cxl_ep *ep)
>  {
>  	put_device(ep->ep);
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 30c80e04cb27..2c6a782d0941 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -871,6 +871,7 @@ bool is_cxl_nvdimm_bridge(struct device *dev);
>  int devm_cxl_add_nvdimm(struct cxl_port *parent_port, struct cxl_memdev *cxlmd);
>  struct cxl_nvdimm_bridge *cxl_find_nvdimm_bridge(struct cxl_port *port);
>  void cxl_region_discovery(struct cxl_port *port);
> +struct cxl_root_decoder *cxl_find_root_decoder(struct cxl_port *port);
>  
>  #ifdef CONFIG_CXL_REGION
>  bool is_cxl_pmem_region(struct device *dev);