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

Jonathan Cameron
2021-02-01T17:23:09Z

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

> From: Dan Williams <dan.j.williams@intel.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@lwn.net>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Ben Widawsky <ben.widawsky@intel.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__ */