Re: [PATCH v6] firmware: google: Implement cbmem in sysfs driver

[Guenter Roeck]

On Tue, Aug 2, 2022 at 7:04 AM Jack Rosenthal <jrosenth@xxxxxxxxxxxx> wrote:
>
> cbmem entries can be read from coreboot table
> 0x31 (LB_TAG_CBMEM_ENTRY).  This commit exports access to cbmem
> entries in sysfs under /sys/firmware/coreboot/cbmem-*.
>
> Link: https://issuetracker.google.com/239604743
> Cc: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> Cc: Guenter Roeck <groeck@xxxxxxxxxxxx>
> Reviewed-by: Julius Werner <jwerner@xxxxxxxxxxxx>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Tested-by: Jack Rosenthal <jrosenth@xxxxxxxxxxxx>
> Signed-off-by: Jack Rosenthal <jrosenth@xxxxxxxxxxxx>

Reviewed-by: Guenter Roeck <groeck@xxxxxxxxxxxx>

> ---
> v6: Modified commit message.
>  .../ABI/testing/sysfs-firmware-coreboot       |  17 ++
>  drivers/firmware/google/Kconfig               |   8 +
>  drivers/firmware/google/Makefile              |   3 +
>  drivers/firmware/google/cbmem.c               | 232 ++++++++++++++++++
>  drivers/firmware/google/coreboot_table.h      |  11 +
>  5 files changed, 271 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-firmware-coreboot
>  create mode 100644 drivers/firmware/google/cbmem.c
>
> diff --git a/Documentation/ABI/testing/sysfs-firmware-coreboot b/Documentation/ABI/testing/sysfs-firmware-coreboot
> new file mode 100644
> index 000000000000..2401483bb86c
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-firmware-coreboot
> @@ -0,0 +1,17 @@
> +What:          /sys/firmware/coreboot/
> +Date:          July 2022
> +Contact:       Jack Rosenthal <jrosenth@xxxxxxxxxxxx>
> +Description:
> +               Coreboot-based BIOS firmware provides a variety of information
> +               in CBMEM.  Each CBMEM entry can be found via Coreboot tables.
> +               For each CBMEM entry, the following are exposed:
> +
> +               ======= =======================================================
> +               address A hexidecimal value of the memory address the data for
> +                       the entry begins at.
> +               size    The size of the data stored.
> +               id      The id corresponding to the entry. A list of ids known
> +                       to coreboot can be found in the coreboot source tree at
> +                       ``src/commonlib/bsd/include/commonlib/bsd/cbmem_id.h``
> +               mem     A file exposing the raw memory for the entry.
> +               ======= =======================================================
> diff --git a/drivers/firmware/google/Kconfig b/drivers/firmware/google/Kconfig
> index 983e07dc022e..bf8316d1cb31 100644
> --- a/drivers/firmware/google/Kconfig
> +++ b/drivers/firmware/google/Kconfig
> @@ -19,6 +19,14 @@ config GOOGLE_SMI
>           driver provides an interface for reading and writing NVRAM
>           variables.
>
> +config GOOGLE_CBMEM
> +       tristate "CBMEM entries in sysfs"
> +       depends on GOOGLE_COREBOOT_TABLE
> +       help
> +         This option enables the kernel to search for Coreboot CBMEM
> +         entries, and expose the memory for each entry in sysfs under
> +         /sys/firmware/coreboot.
> +
>  config GOOGLE_COREBOOT_TABLE
>         tristate "Coreboot Table Access"
>         depends on HAS_IOMEM && (ACPI || OF)
> diff --git a/drivers/firmware/google/Makefile b/drivers/firmware/google/Makefile
> index d17caded5d88..8151e323cc43 100644
> --- a/drivers/firmware/google/Makefile
> +++ b/drivers/firmware/google/Makefile
> @@ -7,5 +7,8 @@ obj-$(CONFIG_GOOGLE_MEMCONSOLE)            += memconsole.o
>  obj-$(CONFIG_GOOGLE_MEMCONSOLE_COREBOOT)   += memconsole-coreboot.o
>  obj-$(CONFIG_GOOGLE_MEMCONSOLE_X86_LEGACY) += memconsole-x86-legacy.o
>
> +# Must come after coreboot_table.o, as this driver depends on that bus type.
> +obj-$(CONFIG_GOOGLE_CBMEM)             += cbmem.o
> +
>  vpd-sysfs-y := vpd.o vpd_decode.o
>  obj-$(CONFIG_GOOGLE_VPD)               += vpd-sysfs.o
> diff --git a/drivers/firmware/google/cbmem.c b/drivers/firmware/google/cbmem.c
> new file mode 100644
> index 000000000000..9646a8047742
> --- /dev/null
> +++ b/drivers/firmware/google/cbmem.c
> @@ -0,0 +1,232 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * cbmem.c
> + *
> + * Driver for exporting cbmem entries in sysfs.
> + *
> + * Copyright 2022 Google LLC
> + */
> +
> +#include <linux/ctype.h>
> +#include <linux/device.h>
> +#include <linux/init.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/kobject.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +#include <linux/sysfs.h>
> +
> +#include "coreboot_table.h"
> +
> +#define LB_TAG_CBMEM_ENTRY 0x31
> +
> +static struct kobject *coreboot_kobj;
> +
> +struct cbmem_entry;
> +struct cbmem_entry_attr {
> +       struct kobj_attribute kobj_attr;
> +       struct cbmem_entry *entry;
> +};
> +
> +struct cbmem_entry {
> +       char *kobj_name;
> +       struct kobject *kobj;
> +       struct coreboot_device *dev;
> +       struct bin_attribute mem_file;
> +       char *mem_file_buf;
> +       struct cbmem_entry_attr address_file;
> +       struct cbmem_entry_attr size_file;
> +       struct cbmem_entry_attr id_file;
> +};
> +
> +static struct cbmem_entry_attr *to_cbmem_entry_attr(struct kobj_attribute *a)
> +{
> +       return container_of(a, struct cbmem_entry_attr, kobj_attr);
> +}
> +
> +static ssize_t cbmem_entry_mem_read(struct file *filp, struct kobject *kobp,
> +                                   struct bin_attribute *bin_attr, char *buf,
> +                                   loff_t pos, size_t count)
> +{
> +       struct cbmem_entry *entry = bin_attr->private;
> +
> +       return memory_read_from_buffer(buf, count, &pos, entry->mem_file_buf,
> +                                      bin_attr->size);
> +}
> +
> +static ssize_t cbmem_entry_mem_write(struct file *filp, struct kobject *kobp,
> +                                    struct bin_attribute *bin_attr, char *buf,
> +                                    loff_t pos, size_t count)
> +{
> +       struct cbmem_entry *entry = bin_attr->private;
> +
> +       if (pos < 0 || pos >= bin_attr->size)
> +               return -EINVAL;
> +       if (count > bin_attr->size - pos)
> +               count = bin_attr->size - pos;
> +
> +       memcpy(entry->mem_file_buf + pos, buf, count);
> +       return count;
> +}
> +
> +static ssize_t cbmem_entry_address_show(struct kobject *kobj,
> +                                       struct kobj_attribute *a, char *buf)
> +{
> +       struct cbmem_entry_attr *entry_attr = to_cbmem_entry_attr(a);
> +
> +       return sysfs_emit(buf, "0x%llx\n",
> +                         entry_attr->entry->dev->cbmem_entry.address);
> +}
> +
> +static ssize_t cbmem_entry_size_show(struct kobject *kobj,
> +                                    struct kobj_attribute *a, char *buf)
> +{
> +       struct cbmem_entry_attr *entry_attr = to_cbmem_entry_attr(a);
> +
> +       return sysfs_emit(buf, "0x%x\n",
> +                         entry_attr->entry->dev->cbmem_entry.entry_size);
> +}
> +
> +static ssize_t cbmem_entry_id_show(struct kobject *kobj,
> +                                  struct kobj_attribute *a, char *buf)
> +{
> +       struct cbmem_entry_attr *entry_attr = to_cbmem_entry_attr(a);
> +
> +       return sysfs_emit(buf, "0x%x\n",
> +                         entry_attr->entry->dev->cbmem_entry.id);
> +}
> +
> +static int cbmem_entry_setup(struct cbmem_entry *entry)
> +{
> +       int ret;
> +
> +       entry->mem_file_buf =
> +               devm_memremap(&entry->dev->dev, entry->dev->cbmem_entry.address,
> +                             entry->dev->cbmem_entry.entry_size, MEMREMAP_WB);
> +       if (!entry->mem_file_buf)
> +               return -ENOMEM;
> +
> +       entry->kobj_name = devm_kasprintf(&entry->dev->dev, GFP_KERNEL,
> +                                         "cbmem-%08x",
> +                                         entry->dev->cbmem_entry.id);
> +       if (!entry->kobj_name)
> +               return -ENOMEM;
> +
> +       entry->kobj = kobject_create_and_add(entry->kobj_name, coreboot_kobj);
> +       if (!entry->kobj)
> +               return -ENOMEM;
> +
> +       sysfs_bin_attr_init(&entry->mem_file);
> +       entry->mem_file.attr.name = "mem";
> +       entry->mem_file.attr.mode = 0664;
> +       entry->mem_file.size = entry->dev->cbmem_entry.entry_size;
> +       entry->mem_file.read = cbmem_entry_mem_read;
> +       entry->mem_file.write = cbmem_entry_mem_write;
> +       entry->mem_file.private = entry;
> +       ret = sysfs_create_bin_file(entry->kobj, &entry->mem_file);
> +       if (ret)
> +               goto free_kobj;
> +
> +       sysfs_attr_init(&entry->address_file.kobj_attr.attr);
> +       entry->address_file.kobj_attr.attr.name = "address";
> +       entry->address_file.kobj_attr.attr.mode = 0444;
> +       entry->address_file.kobj_attr.show = cbmem_entry_address_show;
> +       entry->address_file.entry = entry;
> +       ret = sysfs_create_file(entry->kobj,
> +                               &entry->address_file.kobj_attr.attr);
> +       if (ret)
> +               goto free_mem_file;
> +
> +       sysfs_attr_init(&entry->size_file.kobj_attr.attr);
> +       entry->size_file.kobj_attr.attr.name = "size";
> +       entry->size_file.kobj_attr.attr.mode = 0444;
> +       entry->size_file.kobj_attr.show = cbmem_entry_size_show;
> +       entry->size_file.entry = entry;
> +       ret = sysfs_create_file(entry->kobj, &entry->size_file.kobj_attr.attr);
> +       if (ret)
> +               goto free_address_file;
> +
> +       sysfs_attr_init(&entry->id_file.kobj_attr.attr);
> +       entry->id_file.kobj_attr.attr.name = "id";
> +       entry->id_file.kobj_attr.attr.mode = 0444;
> +       entry->id_file.kobj_attr.show = cbmem_entry_id_show;
> +       entry->id_file.entry = entry;
> +       ret = sysfs_create_file(entry->kobj, &entry->id_file.kobj_attr.attr);
> +       if (ret)
> +               goto free_size_file;
> +
> +       return 0;
> +
> +free_size_file:
> +       sysfs_remove_file(entry->kobj, &entry->size_file.kobj_attr.attr);
> +free_address_file:
> +       sysfs_remove_file(entry->kobj, &entry->address_file.kobj_attr.attr);
> +free_mem_file:
> +       sysfs_remove_bin_file(entry->kobj, &entry->mem_file);
> +free_kobj:
> +       kobject_put(entry->kobj);
> +       return ret;
> +}
> +
> +static int cbmem_entry_probe(struct coreboot_device *dev)
> +{
> +       struct cbmem_entry *entry;
> +
> +       entry = devm_kzalloc(&dev->dev, sizeof(*entry), GFP_KERNEL);
> +       if (!entry)
> +               return -ENOMEM;
> +
> +       dev_set_drvdata(&dev->dev, entry);
> +       entry->dev = dev;
> +       return cbmem_entry_setup(entry);
> +}
> +
> +static void cbmem_entry_remove(struct coreboot_device *dev)
> +{
> +       struct cbmem_entry *entry = dev_get_drvdata(&dev->dev);
> +
> +       sysfs_remove_bin_file(entry->kobj, &entry->mem_file);
> +       sysfs_remove_file(entry->kobj, &entry->address_file.kobj_attr.attr);
> +       sysfs_remove_file(entry->kobj, &entry->size_file.kobj_attr.attr);
> +       sysfs_remove_file(entry->kobj, &entry->id_file.kobj_attr.attr);
> +       kobject_put(entry->kobj);
> +}
> +
> +static struct coreboot_driver cbmem_entry_driver = {
> +       .probe = cbmem_entry_probe,
> +       .remove = cbmem_entry_remove,
> +       .drv = {
> +               .name = "cbmem",
> +       },
> +       .tag = LB_TAG_CBMEM_ENTRY,
> +};
> +
> +static int __init cbmem_init(void)
> +{
> +       int ret;
> +
> +       coreboot_kobj = kobject_create_and_add("coreboot", firmware_kobj);
> +       if (!coreboot_kobj)
> +               return -ENOMEM;
> +
> +       ret = coreboot_driver_register(&cbmem_entry_driver);
> +       if (ret) {
> +               kobject_put(coreboot_kobj);
> +               return ret;
> +       }
> +
> +       return 0;
> +}
> +module_init(cbmem_init);
> +
> +static void __exit cbmem_exit(void)
> +{
> +       kobject_put(coreboot_kobj);
> +       coreboot_driver_unregister(&cbmem_entry_driver);
> +}
> +module_exit(cbmem_exit);
> +
> +MODULE_AUTHOR("Jack Rosenthal <jrosenth@xxxxxxxxxxxx>");
> +MODULE_LICENSE("GPL");
> diff --git a/drivers/firmware/google/coreboot_table.h b/drivers/firmware/google/coreboot_table.h
> index beb778674acd..6c03a8852d1b 100644
> --- a/drivers/firmware/google/coreboot_table.h
> +++ b/drivers/firmware/google/coreboot_table.h
> @@ -39,6 +39,16 @@ struct lb_cbmem_ref {
>         u64 cbmem_addr;
>  };
>
> +/* Corresponds to LB_TAG_CBMEM_ENTRY. */
> +struct lb_cbmem_entry {
> +       u32 tag;
> +       u32 size;
> +
> +       u64 address;
> +       u32 entry_size;
> +       u32 id;
> +};
> +
>  /* Describes framebuffer setup by coreboot */
>  struct lb_framebuffer {
>         u32 tag;
> @@ -65,6 +75,7 @@ struct coreboot_device {
>         union {
>                 struct coreboot_table_entry entry;
>                 struct lb_cbmem_ref cbmem_ref;
> +               struct lb_cbmem_entry cbmem_entry;
>                 struct lb_framebuffer framebuffer;
>         };
>  };
> --
> 2.37.1.455.g008518b4e5-goog
>