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Date: Sun, 19 Apr 2020 19:07:40 -0500
From: Samuel Holland <samuel@...lland.org>
To: patrick.rudolph@...ements.com, linux-kernel@...r.kernel.org
Cc: coreboot@...eboot.org, Thomas Gleixner <tglx@...utronix.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Alexios Zavras <alexios.zavras@...el.com>,
Allison Randal <allison@...utok.net>,
Julius Werner <jwerner@...omium.org>,
Stephen Boyd <swboyd@...omium.org>
Subject: Re: [PATCH v4 1/2] firmware: google: Expose CBMEM over sysfs
On 4/7/20 3:29 AM, patrick.rudolph@...ements.com wrote:
> From: Patrick Rudolph <patrick.rudolph@...ements.com>
>
> Make all CBMEM buffers available to userland. This is useful for tools
> that are currently using /dev/mem.
>
> Make the id, size and address available, as well as the raw table data.
>
> Tools can easily scan the right CBMEM buffer by reading
> /sys/bus/coreboot/drivers/cbmem/coreboot*/cbmem_attributes/id
> or
> /sys/bus/coreboot/devices/coreboot*/cbmem_attributes/id
>
> The binary table data can then be read from
> /sys/bus/coreboot/drivers/cbmem/coreboot*/cbmem_attributes/data
> or
> /sys/bus/coreboot/devices/coreboot*/cbmem_attributes/data
>
> Signed-off-by: Patrick Rudolph <patrick.rudolph@...ements.com>
> ---
> -v2:
> - Add ABI documentation
> - Add 0x prefix on hex values
> -v3:
> - Use BIN_ATTR_RO
> -v4:
> - Use temporary memremap instead of persistent ioremap
> - Constify a struct
> - Get rid of unused headers
> - Use dev_{get|set}_drvdata
> - Use dev_groups to automatically handle attributes
> - Updated file description
> - Updated ABI documentation
> ---
> Documentation/ABI/stable/sysfs-bus-coreboot | 44 +++++++
> drivers/firmware/google/Kconfig | 9 ++
> drivers/firmware/google/Makefile | 1 +
> drivers/firmware/google/cbmem-coreboot.c | 128 ++++++++++++++++++++
> drivers/firmware/google/coreboot_table.h | 14 +++
> 5 files changed, 196 insertions(+)
> create mode 100644 Documentation/ABI/stable/sysfs-bus-coreboot
> create mode 100644 drivers/firmware/google/cbmem-coreboot.c
>
> diff --git a/Documentation/ABI/stable/sysfs-bus-coreboot b/Documentation/ABI/stable/sysfs-bus-coreboot
> new file mode 100644
> index 000000000000..6055906f41f2
> --- /dev/null
> +++ b/Documentation/ABI/stable/sysfs-bus-coreboot
> @@ -0,0 +1,44 @@
> +What: /sys/bus/coreboot/devices/.../cbmem_attributes/id
> +Date: Apr 2020
> +KernelVersion: 5.6
I guess these will be 5.8 now.
> +Contact: Patrick Rudolph <patrick.rudolph@...ements.com>
> +Description:
> + coreboot device directory can contain a file named
> + cbmem_attributes/id if the device corresponds to a CBMEM
> + buffer.
> + The file holds an ASCII representation of the CBMEM ID in hex
> + (e.g. 0xdeadbeef).
> +
> +What: /sys/bus/coreboot/devices/.../cbmem_attributes/size
> +Date: Apr 2020
> +KernelVersion: 5.6
> +Contact: Patrick Rudolph <patrick.rudolph@...ements.com>
> +Description:
> + coreboot device directory can contain a file named
> + cbmem_attributes/size if the device corresponds to a CBMEM
> + buffer.
> + The file holds an representation as decimal number of the
nit: "a representation" (maybe "a decimal representation"?)
> + CBMEM buffer size (e.g. 64).
> +
> +What: /sys/bus/coreboot/devices/.../cbmem_attributes/address
> +Date: Apr 2020
> +KernelVersion: 5.6
> +Contact: Patrick Rudolph <patrick.rudolph@...ements.com>
> +Description:
> + coreboot device directory can contain a file named
> + cbmem_attributes/address if the device corresponds to a CBMEM
> + buffer.
> + The file holds an ASCII representation of the physical address
> + of the CBMEM buffer in hex (e.g. 0x000000008000d000) and should
> + be used for debugging only.
> +
> +What: /sys/bus/coreboot/devices/.../cbmem_attributes/data
> +Date: Apr 2020
> +KernelVersion: 5.6
> +Contact: Patrick Rudolph <patrick.rudolph@...ements.com>
> +Description:
> + coreboot device directory can contain a file named
> + cbmem_attributes/data if the device corresponds to a CBMEM
> + buffer.
> + The file holds a read-only binary representation of the CBMEM
> + buffer.
> diff --git a/drivers/firmware/google/Kconfig b/drivers/firmware/google/Kconfig
> index a3a6ca659ffa..11a67c397ab3 100644
> --- a/drivers/firmware/google/Kconfig
> +++ b/drivers/firmware/google/Kconfig
> @@ -58,6 +58,15 @@ config GOOGLE_FRAMEBUFFER_COREBOOT
> This option enables the kernel to search for a framebuffer in
> the coreboot table. If found, it is registered with simplefb.
>
> +config GOOGLE_CBMEM_COREBOOT
> + tristate "Coreboot CBMEM access"
> + depends on GOOGLE_COREBOOT_TABLE
> + help
> + This option exposes all available CBMEM buffers to userland.
> + The CBMEM id, size and address as well as the raw table data
> + are exported as sysfs attributes of the corresponding coreboot
> + table.
> +
> config GOOGLE_MEMCONSOLE_COREBOOT
> tristate "Firmware Memory Console"
> depends on GOOGLE_COREBOOT_TABLE
> diff --git a/drivers/firmware/google/Makefile b/drivers/firmware/google/Makefile
> index d17caded5d88..62053cd6d058 100644
> --- a/drivers/firmware/google/Makefile
> +++ b/drivers/firmware/google/Makefile
> @@ -2,6 +2,7 @@
>
> obj-$(CONFIG_GOOGLE_SMI) += gsmi.o
> obj-$(CONFIG_GOOGLE_COREBOOT_TABLE) += coreboot_table.o
> +obj-$(CONFIG_GOOGLE_CBMEM_COREBOOT) += cbmem-coreboot.o
> obj-$(CONFIG_GOOGLE_FRAMEBUFFER_COREBOOT) += framebuffer-coreboot.o
> obj-$(CONFIG_GOOGLE_MEMCONSOLE) += memconsole.o
> obj-$(CONFIG_GOOGLE_MEMCONSOLE_COREBOOT) += memconsole-coreboot.o
> diff --git a/drivers/firmware/google/cbmem-coreboot.c b/drivers/firmware/google/cbmem-coreboot.c
> new file mode 100644
> index 000000000000..f76704a6eec7
> --- /dev/null
> +++ b/drivers/firmware/google/cbmem-coreboot.c
> @@ -0,0 +1,128 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * cbmem-coreboot.c
> + *
> + * Exports CBMEM as attributes in sysfs.
> + *
> + * Copyright 2012-2013 David Herrmann <dh.herrmann@...il.com>
> + * Copyright 2017 Google Inc.
> + * Copyright 2019 9elements Agency GmbH
> + */
> +
> +#include <linux/device.h>
> +#include <linux/kernel.h>
> +#include <linux/string.h>
> +#include <linux/module.h>
> +#include <linux/io.h>
> +
> +#include "coreboot_table.h"
> +
> +#define CB_TAG_CBMEM_ENTRY 0x31
> +
> +struct cb_priv {
> + struct lb_cbmem_entry entry;
> +};
> +
> +static ssize_t id_show(struct device *dev,
> + struct device_attribute *attr, char *buffer)
> +{
> + const struct cb_priv *priv = dev_get_drvdata(dev);
> +
> + return sprintf(buffer, "%#08x\n", priv->entry.id);
> +}
> +
> +static ssize_t size_show(struct device *dev,
> + struct device_attribute *attr, char *buffer)
> +{
> + const struct cb_priv *priv = dev_get_drvdata(dev);
> +
> + return sprintf(buffer, "%u\n", priv->entry.entry_size);
> +}
> +
> +static ssize_t address_show(struct device *dev,
> + struct device_attribute *attr, char *buffer)
> +{
> + const struct cb_priv *priv = dev_get_drvdata(dev);
> +
> + return sprintf(buffer, "%#016llx\n", priv->entry.address);
> +}
> +
> +static DEVICE_ATTR_RO(id);
> +static DEVICE_ATTR_RO(size);
> +static DEVICE_ATTR_RO(address);
> +
> +static struct attribute *cb_mem_attrs[] = {
> + &dev_attr_address.attr,
> + &dev_attr_id.attr,
> + &dev_attr_size.attr,
> + NULL
> +};
> +
> +static ssize_t data_read(struct file *filp, struct kobject *kobj,
> + struct bin_attribute *bin_attr,
> + char *buffer, loff_t offset, size_t count)
> +{
> + const struct device *dev = kobj_to_dev(kobj);
> + const struct cb_priv *priv = dev_get_drvdata(dev);
> + void *ptr;
> +
> + /* CBMEM is always RAM with unknown caching attributes. */
> + ptr = memremap(priv->entry.address, priv->entry.entry_size,
> + MEMREMAP_WB | MEMREMAP_WT);
> + if (!ptr)
> + return -ENOMEM;
> +
> + count = memory_read_from_buffer(buffer, count, &offset, ptr,
> + priv->entry.entry_size);
> + memunmap(ptr);
> +
> + return count;
> +}
> +
> +static BIN_ATTR_RO(data, 0);
> +
> +static struct bin_attribute *cb_mem_bin_attrs[] = {
> + &bin_attr_data,
> + NULL
> +};
> +
> +static const struct attribute_group cb_mem_attr_group = {
> + .name = "cbmem_attributes",
> + .attrs = cb_mem_attrs,
> + .bin_attrs = cb_mem_bin_attrs,
> +};
> +
> +static const struct attribute_group *attribute_groups[] = {
> + &cb_mem_attr_group,
> + NULL,
> +};
> +
> +static int cbmem_probe(struct coreboot_device *cdev)
> +{
> + struct device *dev = &cdev->dev;
> + struct cb_priv *priv;
> +
> + priv = devm_kmalloc(dev, sizeof(*priv), GFP_KERNEL);
> + if (!priv)
> + return -ENOMEM;
> +
> + memcpy(&priv->entry, &cdev->cbmem_entry, sizeof(priv->entry));
I don't think it is necessary to create a second copy of the table entry, when
it is already available at cdev->cbmem_entry. You could do:
dev_set_drvdata(dev, cdev);
and that removes the need for struct cb_priv.
Otherwise,
Reviewed-by: Samuel Holland <samuel@...lland.org>
Tested-by: Samuel Holland <samuel@...lland.org>
I hacked nvramtool to pull the CMOS layout from
/sys/bus/coreboot/devices/coreboot0/attributes/data, and that seemed to work.
Cheers,
Samuel
> +
> + dev_set_drvdata(dev, priv);
> +
> + return 0;
> +}
> +
> +static struct coreboot_driver cbmem_driver = {
> + .probe = cbmem_probe,
> + .drv = {
> + .name = "cbmem",
> + .dev_groups = attribute_groups,
> + },
> + .tag = CB_TAG_CBMEM_ENTRY,
> +};
> +
> +module_coreboot_driver(cbmem_driver);
> +
> +MODULE_AUTHOR("9elements Agency GmbH");
> +MODULE_LICENSE("GPL");
> diff --git a/drivers/firmware/google/coreboot_table.h b/drivers/firmware/google/coreboot_table.h
> index 7b7b4a6eedda..fc20b8649882 100644
> --- a/drivers/firmware/google/coreboot_table.h
> +++ b/drivers/firmware/google/coreboot_table.h
> @@ -59,6 +59,19 @@ struct lb_framebuffer {
> u8 reserved_mask_size;
> };
>
> +/*
> + * There can be more than one of these records as there is one per cbmem entry.
> + * Describes a buffer in memory containing runtime data.
> + */
> +struct lb_cbmem_entry {
> + u32 tag;
> + u32 size;
> +
> + u64 address;
> + u32 entry_size;
> + u32 id;
> +};
> +
> /* A device, additionally with information from coreboot. */
> struct coreboot_device {
> struct device dev;
> @@ -66,6 +79,7 @@ struct coreboot_device {
> struct coreboot_table_entry entry;
> struct lb_cbmem_ref cbmem_ref;
> struct lb_framebuffer framebuffer;
> + struct lb_cbmem_entry cbmem_entry;
> };
> };
>
>
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