linux-kernel - Re: [PATCH 01/14] cxl/mem: Introduce a driver for CXL-2.0-Type-3 endpoints

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Date:   Mon, 1 Feb 2021 17:21:18 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Ben Widawsky <ben.widawsky@...el.com>
CC:     <linux-cxl@...r.kernel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Jonathan Corbet <corbet@....net>, <linux-acpi@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-nvdimm@...ts.01.org>,
        <linux-pci@...r.kernel.org>, Bjorn Helgaas <helgaas@...nel.org>,
        "Chris Browy" <cbrowy@...ry-design.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Ira Weiny" <ira.weiny@...el.com>,
        Jon Masters <jcm@...masters.org>,
        "Rafael Wysocki" <rafael.j.wysocki@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        <daniel.lll@...baba-inc.com>,
        "John Groves (jgroves)" <jgroves@...ron.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>
Subject: Re: [PATCH 01/14] cxl/mem: Introduce a driver for CXL-2.0-Type-3
 endpoints

On Fri, 29 Jan 2021 16:24:25 -0800
Ben Widawsky <ben.widawsky@...el.com> wrote:

> From: Dan Williams <dan.j.williams@...el.com>
> 
> The CXL.mem protocol allows a device to act as a provider of "System
> RAM" and/or "Persistent Memory" that is fully coherent as if the memory
> was attached to the typical CPU memory controller.
> 
> With the CXL-2.0 specification a PCI endpoint can implement a "Type-3"
> device interface and give the operating system control over "Host
> Managed Device Memory". See section 2.3 Type 3 CXL Device.
> 
> The memory range exported by the device may optionally be described by
> the platform firmware memory map, or by infrastructure like LIBNVDIMM to
> provision persistent memory capacity from one, or more, CXL.mem devices.
> 
> A pre-requisite for Linux-managed memory-capacity provisioning is this
> cxl_mem driver that can speak the mailbox protocol defined in section
> 8.2.8.4 Mailbox Registers.
> 
> For now just land the initial driver boiler-plate and Documentation/
> infrastructure.
> 
> Link: https://www.computeexpresslink.org/download-the-specification
> Cc: Jonathan Corbet <corbet@....net>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>
Hi Ben,

One thing below about using defs from generic PCI headers where
they are not CXL specific.


> diff --git a/drivers/cxl/pci.h b/drivers/cxl/pci.h
> new file mode 100644
> index 000000000000..a8a9935fa90b
> --- /dev/null
> +++ b/drivers/cxl/pci.h
> @@ -0,0 +1,20 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/* Copyright(c) 2020 Intel Corporation. All rights reserved. */
> +#ifndef __CXL_PCI_H__
> +#define __CXL_PCI_H__
> +
> +#define PCI_CLASS_MEMORY_CXL	0x050210
> +
> +/*
> + * See section 8.1 Configuration Space Registers in the CXL 2.0
> + * Specification
> + */
> +#define PCI_EXT_CAP_ID_DVSEC		0x23
> +#define PCI_DVSEC_VENDOR_ID_CXL		0x1E98
> +#define PCI_DVSEC_VENDOR_ID_OFFSET	0x4
> +#define PCI_DVSEC_ID_CXL		0x0
> +#define PCI_DVSEC_ID_OFFSET		0x8

include/uapi/linux/pci-regs.h includes equivalents of generic parts of
this already though PCI_DVSEC_HEADER1 isn't exactly informative naming.

> +
> +#define PCI_DVSEC_ID_CXL_REGLOC		0x8
> +
> +#endif /* __CXL_PCI_H__ */