Re: [PATCH v2 1/8] cxl/mem: Introduce a driver for CXL-2.0-Type-3 endpoints

[Ben Widawsky]

On 21-02-10 16:17:07, Jonathan Cameron wrote:
> On Tue, 9 Feb 2021 16:02:52 -0800
> Ben Widawsky <ben.widawsky@xxxxxxxxx> wrote:
> 
> > From: Dan Williams <dan.j.williams@xxxxxxxxx>
> > 
> > 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@xxxxxxx>
> > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Signed-off-by: Ben Widawsky <ben.widawsky@xxxxxxxxx>
> > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> (v1)
> 
> A few trivial bits inline but nothing that I feel that strongly about.
> It is probably a good idea to add a note about generic dvsec code
> somewhere in this patch description (to avoid people raising it on
> future versions!)
> 
> With the define of PCI_EXT_CAP_ID_DVSEC dropped (it's in the generic
> header already).
> 
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> 
> > ---
> >  Documentation/driver-api/cxl/index.rst        | 12 ++++
> >  .../driver-api/cxl/memory-devices.rst         | 29 +++++++++
> >  Documentation/driver-api/index.rst            |  1 +
> >  drivers/Kconfig                               |  1 +
> >  drivers/Makefile                              |  1 +
> >  drivers/cxl/Kconfig                           | 35 +++++++++++
> >  drivers/cxl/Makefile                          |  4 ++
> >  drivers/cxl/mem.c                             | 63 +++++++++++++++++++
> >  drivers/cxl/pci.h                             | 18 ++++++
> >  include/linux/pci_ids.h                       |  1 +
> >  10 files changed, 165 insertions(+)
> >  create mode 100644 Documentation/driver-api/cxl/index.rst
> >  create mode 100644 Documentation/driver-api/cxl/memory-devices.rst
> >  create mode 100644 drivers/cxl/Kconfig
> >  create mode 100644 drivers/cxl/Makefile
> >  create mode 100644 drivers/cxl/mem.c
> >  create mode 100644 drivers/cxl/pci.h
> > 
> > diff --git a/Documentation/driver-api/cxl/index.rst b/Documentation/driver-api/cxl/index.rst
> > new file mode 100644
> > index 000000000000..036e49553542
> > --- /dev/null
> > +++ b/Documentation/driver-api/cxl/index.rst
> > @@ -0,0 +1,12 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +====================
> > +Compute Express Link
> > +====================
> > +
> > +.. toctree::
> > +   :maxdepth: 1
> > +
> > +   memory-devices
> > +
> > +.. only::  subproject and html
> > diff --git a/Documentation/driver-api/cxl/memory-devices.rst b/Documentation/driver-api/cxl/memory-devices.rst
> > new file mode 100644
> > index 000000000000..43177e700d62
> > --- /dev/null
> > +++ b/Documentation/driver-api/cxl/memory-devices.rst
> > @@ -0,0 +1,29 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +.. include:: <isonum.txt>
> > +
> > +===================================
> > +Compute Express Link Memory Devices
> > +===================================
> > +
> > +A Compute Express Link Memory Device is a CXL component that implements the
> > +CXL.mem protocol. It contains some amount of volatile memory, persistent memory,
> > +or both. It is enumerated as a PCI device for configuration and passing
> > +messages over an MMIO mailbox. Its contribution to the System Physical
> > +Address space is handled via HDM (Host Managed Device Memory) decoders
> > +that optionally define a device's contribution to an interleaved address
> > +range across multiple devices underneath a host-bridge or interleaved
> > +across host-bridges.
> > +
> > +Driver Infrastructure
> > +=====================
> > +
> > +This section covers the driver infrastructure for a CXL memory device.
> > +
> > +CXL Memory Device
> > +-----------------
> > +
> > +.. kernel-doc:: drivers/cxl/mem.c
> > +   :doc: cxl mem
> > +
> > +.. kernel-doc:: drivers/cxl/mem.c
> > +   :internal:
> > diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst
> > index 2456d0a97ed8..d246a18fd78f 100644
> > --- a/Documentation/driver-api/index.rst
> > +++ b/Documentation/driver-api/index.rst
> > @@ -35,6 +35,7 @@ available subsections can be seen below.
> >     usb/index
> >     firewire
> >     pci/index
> > +   cxl/index
> >     spi
> >     i2c
> >     ipmb
> > diff --git a/drivers/Kconfig b/drivers/Kconfig
> > index dcecc9f6e33f..62c753a73651 100644
> > --- a/drivers/Kconfig
> > +++ b/drivers/Kconfig
> > @@ -6,6 +6,7 @@ menu "Device Drivers"
> >  source "drivers/amba/Kconfig"
> >  source "drivers/eisa/Kconfig"
> >  source "drivers/pci/Kconfig"
> > +source "drivers/cxl/Kconfig"
> >  source "drivers/pcmcia/Kconfig"
> >  source "drivers/rapidio/Kconfig"
> >  
> > diff --git a/drivers/Makefile b/drivers/Makefile
> > index fd11b9ac4cc3..678ea810410f 100644
> > --- a/drivers/Makefile
> > +++ b/drivers/Makefile
> > @@ -73,6 +73,7 @@ obj-$(CONFIG_NVM)		+= lightnvm/
> >  obj-y				+= base/ block/ misc/ mfd/ nfc/
> >  obj-$(CONFIG_LIBNVDIMM)		+= nvdimm/
> >  obj-$(CONFIG_DAX)		+= dax/
> > +obj-$(CONFIG_CXL_BUS)		+= cxl/
> >  obj-$(CONFIG_DMA_SHARED_BUFFER) += dma-buf/
> >  obj-$(CONFIG_NUBUS)		+= nubus/
> >  obj-y				+= macintosh/
> > diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
> > new file mode 100644
> > index 000000000000..9e80b311e928
> > --- /dev/null
> > +++ b/drivers/cxl/Kconfig
> > @@ -0,0 +1,35 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +menuconfig CXL_BUS
> > +	tristate "CXL (Compute Express Link) Devices Support"
> > +	depends on PCI
> > +	help
> > +	  CXL is a bus that is electrically compatible with PCI Express, but
> > +	  layers three protocols on that signalling (CXL.io, CXL.cache, and
> > +	  CXL.mem). The CXL.cache protocol allows devices to hold cachelines
> > +	  locally, the CXL.mem protocol allows devices to be fully coherent
> > +	  memory targets, the CXL.io protocol is equivalent to PCI Express.
> > +	  Say 'y' to enable support for the configuration and management of
> > +	  devices supporting these protocols.
> > +
> > +if CXL_BUS
> > +
> > +config CXL_MEM
> > +	tristate "CXL.mem: Memory Devices"
> > +	help
> > +	  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.
> > +
> > +	  Say 'y/m' to enable a driver (named "cxl_mem.ko" when built as
> > +	  a module) that will attach to CXL.mem devices for
> > +	  configuration, provisioning, and health monitoring. This
> > +	  driver is required for dynamic provisioning of CXL.mem
> > +	  attached memory which is a prerequisite for persistent memory
> > +	  support. Typically volatile memory is mapped by platform
> > +	  firmware and included in the platform memory map, but in some
> > +	  cases the OS is responsible for mapping that memory. See
> > +	  Chapter 2.3 Type 3 CXL Device in the CXL 2.0 specification.
> > +
> > +	  If unsure say 'm'.
> > +endif
> > diff --git a/drivers/cxl/Makefile b/drivers/cxl/Makefile
> > new file mode 100644
> > index 000000000000..4a30f7c3fc4a
> > --- /dev/null
> > +++ b/drivers/cxl/Makefile
> > @@ -0,0 +1,4 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +obj-$(CONFIG_CXL_MEM) += cxl_mem.o
> > +
> > +cxl_mem-y := mem.o
> > diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> > new file mode 100644
> > index 000000000000..99a6571508df
> > --- /dev/null
> > +++ b/drivers/cxl/mem.c
> > @@ -0,0 +1,63 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/* Copyright(c) 2020 Intel Corporation. All rights reserved. */
> > +#include <linux/module.h>
> > +#include <linux/pci.h>
> > +#include <linux/io.h>
> > +#include "pci.h"
> > +
> > +static int cxl_mem_dvsec(struct pci_dev *pdev, int dvsec)
> > +{
> > +	int pos;
> > +
> > +	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_DVSEC);
> > +	if (!pos)
> > +		return 0;
> > +
> > +	while (pos) {
> > +		u16 vendor, id;
> > +
> > +		pci_read_config_word(pdev, pos + PCI_DVSEC_HEADER1, &vendor);
> > +		pci_read_config_word(pdev, pos + PCI_DVSEC_HEADER2, &id);
> > +		if (vendor == PCI_DVSEC_VENDOR_ID_CXL && dvsec == id)
> > +			return pos;
> > +
> > +		pos = pci_find_next_ext_capability(pdev, pos,
> > +						   PCI_EXT_CAP_ID_DVSEC);
> > +	}
> > +
> > +	return 0;
> 
> Christopher Hellwig raised this in v1. 
> 
> https://lore.kernel.org/linux-pci/20201104201141.GA399378@bjorn-Precision-5520/
> 
> +CC Dave Jiang for update on that.
> 
> This wants to move towards a generic helper.  We can do the deduplication
> later as Bjorn suggested.
> 
> > +}
> > +
> > +static int cxl_mem_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> > +{
> > +	struct device *dev = &pdev->dev;
> > +	int regloc;
> > +
> > +	regloc = cxl_mem_dvsec(pdev, PCI_DVSEC_ID_CXL_REGLOC_OFFSET);
> > +	if (!regloc) {
> > +		dev_err(dev, "register location dvsec not found\n");
> > +		return -ENXIO;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct pci_device_id cxl_mem_pci_tbl[] = {
> > +	/* PCI class code for CXL.mem Type-3 Devices */
> > +	{ PCI_ANY_ID, PCI_ANY_ID, PCI_ANY_ID, PCI_ANY_ID,
> > +	  PCI_CLASS_MEMORY_CXL << 8 | CXL_MEMORY_PROGIF, 0xffffff, 0 },
> 
> Having looked at this and thought 'thats a bit tricky to check'
> I did a quick grep and seems the kernel is split between this approach
> and people going with the mor readable c99 style initiators
> 	.class = .. etc
> 
> Personally I'd find the c99 approach easier to read. 
> 

Well, it's Dan's patch, but I did modify this last. I took a look around, and
the best fit seems to me seems to be:
-       { PCI_ANY_ID, PCI_ANY_ID, PCI_ANY_ID, PCI_ANY_ID,
-         PCI_CLASS_MEMORY_CXL << 8 | CXL_MEMORY_PROGIF, 0xffffff, 0 },
+       { PCI_DEVICE_CLASS((PCI_CLASS_MEMORY_CXL << 8 | CXL_MEMORY_PROGIF), ~0)},

That work for you?

> > +	{ /* terminate list */ },
> > +};
> > +MODULE_DEVICE_TABLE(pci, cxl_mem_pci_tbl);
> > +
> > +static struct pci_driver cxl_mem_driver = {
> > +	.name			= KBUILD_MODNAME,
> > +	.id_table		= cxl_mem_pci_tbl,
> > +	.probe			= cxl_mem_probe,
> > +	.driver	= {
> > +		.probe_type	= PROBE_PREFER_ASYNCHRONOUS,
> > +	},
> > +};
> > +
> > +MODULE_LICENSE("GPL v2");
> > +module_pci_driver(cxl_mem_driver);
> > diff --git a/drivers/cxl/pci.h b/drivers/cxl/pci.h
> > new file mode 100644
> > index 000000000000..f135b9f7bb21
> > --- /dev/null
> > +++ b/drivers/cxl/pci.h
> > @@ -0,0 +1,18 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/* Copyright(c) 2020 Intel Corporation. All rights reserved. */
> > +#ifndef __CXL_PCI_H__
> > +#define __CXL_PCI_H__
> > +
> > +#define CXL_MEMORY_PROGIF	0x10
> > +
> > +/*
> > + * See section 8.1 Configuration Space Registers in the CXL 2.0
> > + * Specification
> > + */
> > +#define PCI_EXT_CAP_ID_DVSEC		0x23
> 
> This is already in include/uapi/linux/pci_regs.h
> 
> > +#define PCI_DVSEC_VENDOR_ID_CXL		0x1E98
> > +#define PCI_DVSEC_ID_CXL		0x0
> > +
> > +#define PCI_DVSEC_ID_CXL_REGLOC_OFFSET		0x8
> > +
> > +#endif /* __CXL_PCI_H__ */
> > diff --git a/include/linux/pci_ids.h b/include/linux/pci_ids.h
> > index d8156a5dbee8..766260a9b247 100644
> > --- a/include/linux/pci_ids.h
> > +++ b/include/linux/pci_ids.h
> > @@ -51,6 +51,7 @@
> >  #define PCI_BASE_CLASS_MEMORY		0x05
> >  #define PCI_CLASS_MEMORY_RAM		0x0500
> >  #define PCI_CLASS_MEMORY_FLASH		0x0501
> > +#define PCI_CLASS_MEMORY_CXL		0x0502
> >  #define PCI_CLASS_MEMORY_OTHER		0x0580
> >  
> >  #define PCI_BASE_CLASS_BRIDGE		0x06
>