Re: [PATCH v3 1/2] firmware: google: Expose CBMEM over sysfs

[Stephen Boyd <swboyd@chromium.org>]

Quoting patrick.rudolph@9elements.com (2019-11-28 04:50:50)
> diff --git a/Documentation/ABI/stable/sysfs-bus-coreboot b/Documentation/ABI/stable/sysfs-bus-coreboot
> new file mode 100644
> index 000000000000..1b04b8abc858
> --- /dev/null
> +++ b/Documentation/ABI/stable/sysfs-bus-coreboot
> @@ -0,0 +1,43 @@
> +What:          /sys/bus/coreboot/devices/.../cbmem_attributes/id
> +Date:          Nov 2019
> +KernelVersion: 5.5
> +Contact:       Patrick Rudolph <patrick.rudolph@9elements.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:          Nov 2019
> +KernelVersion: 5.5
> +Contact:       Patrick Rudolph <patrick.rudolph@9elements.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
> +               CBMEM buffer size (e.g. 64).
> +
> +What:          /sys/bus/coreboot/devices/.../cbmem_attributes/address
> +Date:          Nov 2019
> +KernelVersion: 5.5
> +Contact:       Patrick Rudolph <patrick.rudolph@9elements.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).

What is the purpose of this field? Can't userspace read the 'data'
attribute to get the data out?

> +
> +What:          /sys/bus/coreboot/devices/.../cbmem_attributes/data
> +Date:          Nov 2019
> +KernelVersion: 5.5
> +Contact:       Patrick Rudolph <patrick.rudolph@9elements.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/cbmem-coreboot.c b/drivers/firmware/google/cbmem-coreboot.c
> new file mode 100644
> index 000000000000..c67651a9c287
> --- /dev/null
> +++ b/drivers/firmware/google/cbmem-coreboot.c
> @@ -0,0 +1,159 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * fmap-coreboot.c
> + *
> + * Exports CBMEM as attributes in sysfs.
> + *
> + * Copyright 2012-2013 David Herrmann <dh.herrmann@gmail.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>

Is this include used? Should probably include linux/memremap.h instead.

> +#include <linux/slab.h>
> +
> +#include "coreboot_table.h"
> +
> +#define CB_TAG_CBMEM_ENTRY 0x31
> +
> +struct cb_priv {
> +       void *remap;
> +       struct lb_cbmem_entry entry;
> +};
> +
> +static ssize_t id_show(struct device *dev,
> +                      struct device_attribute *attr, char *buffer)
> +{
> +       const struct cb_priv *priv;
> +
> +       priv = (const struct cb_priv *)dev_get_platdata(dev);

Please drop useless casts from void *.

> +
> +       return sprintf(buffer, "0x%08x\n", priv->entry.id);

Use %#08x. Also not sure we need newlines but I guess it's OK.

> +}
> +
> +static ssize_t size_show(struct device *dev,
> +                        struct device_attribute *attr, char *buffer)
> +{
> +       const struct cb_priv *priv;
> +
> +       priv = (const struct cb_priv *)dev_get_platdata(dev);
> +
> +       return sprintf(buffer, "%u\n", priv->entry.size);
> +}
> +
> +static ssize_t address_show(struct device *dev,
> +                           struct device_attribute *attr, char *buffer)
> +{
> +       const struct cb_priv *priv;
> +
> +       priv = (const struct cb_priv *)dev_get_platdata(dev);
> +
> +       return sprintf(buffer, "0x%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)
> +{
> +       struct device *dev = kobj_to_dev(kobj);
> +       const struct cb_priv *priv;
> +
> +       priv = (const struct cb_priv *)dev_get_platdata(dev);
> +
> +       return memory_read_from_buffer(buffer, count, &offset,
> +                                      priv->remap, priv->entry.size);
> +}
> +
> +static BIN_ATTR_RO(data, 0);
> +
> +static struct bin_attribute *cb_mem_bin_attrs[] = {
> +       &bin_attr_data,
> +       NULL
> +};
> +
> +static struct attribute_group cb_mem_attr_group = {

Can it be const?

> +       .name = "cbmem_attributes",
> +       .attrs = cb_mem_attrs,
> +       .bin_attrs = cb_mem_bin_attrs,
> +};
> +
> +static int cbmem_probe(struct coreboot_device *cdev)
> +{
> +       struct device *dev = &cdev->dev;
> +       struct cb_priv *priv;
> +       int err;
> +
> +       priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> +       if (!priv)
> +               return -ENOMEM;
> +
> +       memcpy(&priv->entry, &cdev->cbmem_entry, sizeof(priv->entry));
> +
> +       priv->remap = memremap(priv->entry.address,
> +                              priv->entry.entry_size, MEMREMAP_WB);
> +       if (!priv->remap) {
> +               err = -ENOMEM;
> +               goto failure;
> +       }
> +
> +       err = sysfs_create_group(&dev->kobj, &cb_mem_attr_group);
> +       if (err) {
> +               dev_err(dev, "failed to create sysfs attributes: %d\n", err);
> +               memunmap(priv->remap);
> +               goto failure;
> +       }
> +
> +       dev->platform_data = priv;

Can we use dev_{set,get}_drvdata() instead?

> +
> +       return 0;
> +failure:
> +       kfree(priv);
> +       return err;
> +}
> +
> +static int cbmem_remove(struct coreboot_device *cdev)
> +{
> +       struct device *dev = &cdev->dev;
> +       const struct cb_priv *priv;
> +
> +       priv = (const struct cb_priv *)dev_get_platdata(dev);
> +
> +       sysfs_remove_group(&dev->kobj, &cb_mem_attr_group);
> +
> +       if (priv)
> +               memunmap(priv->remap);
> +       kfree(priv);
> +
> +       dev->platform_data = NULL;

This shouldn't be necessary if the driver_data APIs are used instead.
The driver core does it for us then.

> +
> +       return 0;
> +}
> +
> +static struct coreboot_driver cbmem_driver = {
> +       .probe = cbmem_probe,
> +       .remove = cbmem_remove,
> +       .drv = {
> +               .name = "cbmem",
> +       },
> +       .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..506048c724d8 100644
> --- a/drivers/firmware/google/coreboot_table.h
> +++ b/drivers/firmware/google/coreboot_table.h
> @@ -59,6 +59,18 @@ struct lb_framebuffer {
>         u8  reserved_mask_size;
>  };
>  
> +/* There can be more than one of these records as there is one per cbmem entry.

Please add a bare /* for multi-line comments.

> + * 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;