linux-kernel - Re: [RFC PATCH v3 08/16] cxl/mem: Register CXL memX devices

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Message-ID: <20210114162822.00002797@Huawei.com>
Date:   Thu, 14 Jan 2021 16:28:22 +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>,
        <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        "linux-acpi@...r.kernel.org, Ira Weiny" <ira.weiny@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Jon Masters <jcm@...masters.org>,
        Chris Browy <cbrowy@...ry-design.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Christoph Hellwig" <hch@...radead.org>,
        <daniel.lll@...baba-inc.com>
Subject: Re: [RFC PATCH v3 08/16] cxl/mem: Register CXL memX devices

On Mon, 11 Jan 2021 14:51:12 -0800
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), and 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.
> 
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>

Don't hide the driver core change inside a patch doing other stuff.
(it is a nice change though!)

Otherwise, just a request for units in the sysfs ABI docs.

Jonathan


> ---
>  Documentation/ABI/testing/sysfs-bus-cxl |  26 +++
>  Documentation/cxl/memory-devices.rst    |   3 +
>  drivers/base/core.c                     |  14 ++
>  drivers/cxl/Makefile                    |   2 +
>  drivers/cxl/bus.c                       |  54 +++++
>  drivers/cxl/bus.h                       |   8 +
>  drivers/cxl/cxl.h                       |   3 +
>  drivers/cxl/mem.c                       | 282 +++++++++++++++++++++++-
>  include/linux/device.h                  |   1 +
>  9 files changed, 392 insertions(+), 1 deletion(-)
>  create mode 100644 Documentation/ABI/testing/sysfs-bus-cxl
>  create mode 100644 drivers/cxl/bus.c
>  create mode 100644 drivers/cxl/bus.h
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> new file mode 100644
> index 000000000000..fe7b87eba988
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -0,0 +1,26 @@
> +What:		/sys/bus/cxl/devices/memX/firmware_version
> +Date:		December, 2020
> +KernelVersion:	v5.12
> +Contact:	linux-cxl@...r.kernel.org
> +Description:
> +		(RO) "FW Revision" string as reported by the Identify
> +		Memory Device Output Payload in the CXL-2.0
> +		specification.
> +
> +What:		/sys/bus/cxl/devices/memX/ram/size
> +Date:		December, 2020
> +KernelVersion:	v5.12
> +Contact:	linux-cxl@...r.kernel.org
> +Description:
> +		(RO) "Volatile Only Capacity" as reported by the
> +		Identify Memory Device Output Payload in the CXL-2.0
> +		specification.

Nice to see the format /units of these described in this doc as well as the spec.
Section number etc also good if you can add it to these docs.

> +
> +What:		/sys/bus/cxl/devices/memX/pmem/size
> +Date:		December, 2020
> +KernelVersion:	v5.12
> +Contact:	linux-cxl@...r.kernel.org
> +Description:
> +		(RO) "Persistent Only Capacity" as reported by the
> +		Identify Memory Device Output Payload in the CXL-2.0
> +		specification.
> diff --git a/Documentation/cxl/memory-devices.rst b/Documentation/cxl/memory-devices.rst
> index 134c9b6b4ff4..5f723c25382b 100644
> --- a/Documentation/cxl/memory-devices.rst
> +++ b/Documentation/cxl/memory-devices.rst
> @@ -37,3 +37,6 @@ External Interfaces
>  
>  .. kernel-doc:: drivers/cxl/acpi.c
>     :export:
> +
> +.. kernel-doc:: drivers/cxl/bus.c
> +   :export:
> 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.
> + */

I like the idea of a nice generic wrapper for this but definitely not
deep inside a patch doing something else.

> +struct device *get_live_device(struct device *dev)
> +{
> +	return dev && !dev->p->dead ? get_device(dev) : NULL;
> +}
> +EXPORT_SYMBOL_GPL(get_live_device);
> +
...