linux-kernel - Re: [PATCH v3 08/15] cxl/pci: Map CXL PCIe root port and downstream switch port RAS registers

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Message-ID:
 <VI1PR10MB201647BD9FC20C8BAB8F4A90CE262@VI1PR10MB2016.EURPRD10.PROD.OUTLOOK.COM>
Date: Sun, 17 Nov 2024 15:45:15 +0800
From: Li Ming <ming4.li@...look.com>
To: Terry Bowman <terry.bowman@....com>, linux-cxl@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
 nifan.cxl@...il.com, ming4.li@...el.com, dave@...olabs.net,
 jonathan.cameron@...wei.com, dave.jiang@...el.com,
 alison.schofield@...el.com, vishal.l.verma@...el.com,
 dan.j.williams@...el.com, bhelgaas@...gle.com, mahesh@...ux.ibm.com,
 ira.weiny@...el.com, oohall@...il.com, Benjamin.Cheatham@....com,
 rrichter@....com, nathan.fontenot@....com,
 Smita.KoralahalliChannabasappa@....com, lukas@...ner.de
Subject: Re: [PATCH v3 08/15] cxl/pci: Map CXL PCIe root port and downstream
 switch port RAS registers



On 2024/11/14 5:54, Terry Bowman wrote:
> The CXL mem driver (cxl_mem) currently maps and caches a pointer to RAS
> registers for the endpoint's root port. The same needs to be done for
> each of the CXL downstream switch ports and CXL root ports found between
> the endpoint and CXL host bridge.
> 
> Introduce cxl_init_ep_ports_aer() to be called for each port in the
> sub-topology between the endpoint and the CXL host bridge. This function
> will determine if there are CXL downstream switch ports or CXL root ports
> associated with this port. The same check will be added in the future for
> upstream switch ports.
> 
> Move the RAS register map logic from cxl_dport_map_ras() into
> cxl_dport_init_ras_reporting(). This eliminates the need for the helper
> function, cxl_dport_map_ras().
> 
> cxl_init_ep_ports_aer() calls cxl_dport_init_ras_reporting() to map
> the RAS registers for CXL downstream switch ports and CXL root ports.
> 
> cxl_dport_init_ras_reporting() must check for previously mapped registers
> before mapping. This is necessary because endpoints under a CXL switch
> may share CXL downstream switch ports or CXL root ports. Ensure the port
> registers are only mapped once.
> 
> Signed-off-by: Terry Bowman <terry.bowman@....com>

[snip]

>   static int devm_cxl_add_endpoint(struct device *host, struct cxl_memdev *cxlmd,
>   				 struct cxl_dport *parent_dport)
>   {
> @@ -62,6 +87,7 @@ static int devm_cxl_add_endpoint(struct device *host, struct cxl_memdev *cxlmd,
>   
>   		ep = cxl_ep_load(iter, cxlmd);
>   		ep->next = down;
> +		cxl_init_ep_ports_aer(ep);

In RCH case, seems like another issue is here, I believe that a RCD will 
be added to a CXL root directly rather than a CXL host bridge, it means 
that no chance to call cxl_init_ep_ports_aer() for a RCD, because this 
loop is only for a EP attaching to a CXL non-root port.

Please correct me if I'm wrong.

Ming

>   	}
>   
>   	/* Note: endpoint port component registers are derived from @cxlds */
> @@ -166,8 +192,6 @@ static int cxl_mem_probe(struct device *dev)
>   	else
>   		endpoint_parent = &parent_port->dev;
>   
> -	cxl_dport_init_ras_reporting(dport, dev);
> -
>   	scoped_guard(device, endpoint_parent) {
>   		if (!endpoint_parent->driver) {
>   			dev_err(dev, "CXL port topology %s not enabled\n",