linux-kernel - Re: [PATCH v6 15/27] cxl/port: Store the port's Component Register mappings in struct cxl

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Date:   Thu, 22 Jun 2023 14:20:01 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Terry Bowman <terry.bowman@....com>
CC:     <alison.schofield@...el.com>, <vishal.l.verma@...el.com>,
        <ira.weiny@...el.com>, <bwidawsk@...nel.org>,
        <dan.j.williams@...el.com>, <dave.jiang@...el.com>,
        <linux-cxl@...r.kernel.org>, <rrichter@....com>,
        <linux-kernel@...r.kernel.org>, <bhelgaas@...gle.com>
Subject: Re: [PATCH v6 15/27] cxl/port: Store the port's Component Register
 mappings in struct cxl_port

On Wed, 21 Jun 2023 22:51:14 -0500
Terry Bowman <terry.bowman@....com> wrote:

> From: Robert Richter <rrichter@....com>
> 
> CXL capabilities are stored in the Component Registers. To use them,
> the specific I/O ranges of the capabilities must be determined by
> probing the registers. For this, the whole Component Register range
> needs to be mapped temporarily to detect the offset and length of a
> capability range.
> 
> In order to use more than one capability of a component (e.g. RAS and
> HDM) the Component Register are probed and its mappings created
> multiple times. This also causes overlapping I/O ranges as the whole
> Component Register range must be mapped again while a capability's I/O
> range is already mapped.
> 
> Different capabilities cannot be setup at the same time. E.g. the RAS
> capability must be made available as soon as the PCI driver is bound,
> the HDM decoder is setup later during port enumeration. Moreover,
> during early setup it is still unknown if a certain capability is
> needed. A central capability setup is therefore not possible,
> capabilities must be individually enabled once needed during
> initialization.
> 
> To avoid a duplicate register probe and overlapping I/O mappings, only
> probe the Component Registers one time and store the Component
> Register mapping in struct port. The stored mappings can be used later
> to iomap the capability register range when enabling the capability,
> which will be implemented in a follow-on patch.
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> Signed-off-by: Terry Bowman <terry.bowman@....com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>