linux-kernel - Re: [PATCH 05/14] cxl/mem: Register CXL memX devices

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Date:   Fri, 29 Jan 2021 16:31:15 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Ben Widawsky <ben.widawsky@...el.com>
Cc:     linux-cxl@...r.kernel.org, Linux ACPI <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux PCI <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>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        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 05/14] cxl/mem: Register CXL memX devices

On Fri, Jan 29, 2021 at 4:25 PM Ben Widawsky <ben.widawsky@...el.com> wrote:
>
> From: Dan Williams <dan.j.williams@...el.com>
>
> Create the /sys/bus/cxl hierarchy to enumerate:
>
> * Memory Devices (per-endpoint control devices)
>
> * Memory Address Space Devices (platform address ranges with
>   interleaving, performance, and persistence attributes)
>
> * Memory Regions (active provisioned memory from an address space device
>   that is in use as System RAM or delegated to libnvdimm as Persistent
>   Memory regions).
>
> For now, only the per-endpoint control devices are registered on the
> 'cxl' bus. However, going forward it will provide a mechanism to
> coordinate cross-device interleave.
>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>
> ---
>  Documentation/ABI/testing/sysfs-bus-cxl       |  26 ++
>  .../driver-api/cxl/memory-devices.rst         |  17 +
>  drivers/base/core.c                           |  14 +
>  drivers/cxl/Makefile                          |   3 +
>  drivers/cxl/bus.c                             |  29 ++
>  drivers/cxl/cxl.h                             |   4 +
>  drivers/cxl/mem.c                             | 308 +++++++++++++++++-
>  include/linux/device.h                        |   1 +
>  8 files changed, 400 insertions(+), 2 deletions(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-bus-cxl
>  create mode 100644 drivers/cxl/bus.c
[..]
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 25e08e5f40bd..33432a4cbe23 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -3179,6 +3179,20 @@ struct device *get_device(struct device *dev)
>  }
>  EXPORT_SYMBOL_GPL(get_device);
>
> +/**
> + * get_live_device() - increment reference count for device iff !dead
> + * @dev: device.
> + *
> + * Forward the call to get_device() if the device is still alive. If
> + * this is called with the device_lock() held then the device is
> + * guaranteed to not die until the device_lock() is dropped.
> + */
> +struct device *get_live_device(struct device *dev)
> +{
> +       return dev && !dev->p->dead ? get_device(dev) : NULL;
> +}
> +EXPORT_SYMBOL_GPL(get_live_device);

Disregard this hunk, it's an abandoned idea that I failed to cleanup.