linux-kernel - Re: [RFC Patch v1 1/3] cxl/core: Fix caching dport GPF DVSEC issue

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Message-ID: <20250321074154.ltenxqprgxizh5kx@offworld>
Date: Fri, 21 Mar 2025 00:41:54 -0700
From: Davidlohr Bueso <dave@...olabs.net>
To: Li Ming <ming.li@...omail.com>
Cc: jonathan.cameron@...wei.com, dave.jiang@...el.com,
	alison.schofield@...el.com, vishal.l.verma@...el.com,
	ira.weiny@...el.com, dan.j.williams@...el.com,
	linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC Patch v1 1/3] cxl/core: Fix caching dport GPF DVSEC issue

On Wed, 19 Mar 2025, Li Ming wrote:

>Per Table 8-2 in CXL r3.2 section 8.1.1 and CXL r3.2 section 8.1.6, only
>CXL Downstream switch ports and CXL root ports have GPF DVSEC for CXL
>Port(DVSEC ID 04h).
>
>CXL subsystem has a gpf_dvsec in struct cxl_port which is used to cache
>the offset of a GPF DVSEC in PCIe configuration space. It will be
>updated during the first EP attaching to the cxl_port, so the gpf_dvsec
>can only cache the GPF DVSEC offset of the dport which the first EP is
>under. Will not have chance to update it during other EPs attaching.
>That means CXL subsystem will use the same GPF DVSEC offset for all
>dports under the port, it will be a problem if the GPF DVSEC offset
>cached in cxl_port is not the right offset for a dport.
>
>Moving gpf_dvsec from struct cxl_port to struct cxl_dport, make every
>cxl dport has their own GPF DVSEC offset caching, and each cxl dport
>uses its own GPF DVSEC offset for GPF DVSEC accessing.

This conversion looks good if necessary.

Reviewed-by: Davidlohr Bueso <dave@...olabs.net>