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Subject[PATCH 5/5] nvmem: Add support for write-only instances
Date
From: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>

There is at least one real-world use-case for write-only nvmem
instances. Refer to 03cd45d2e219 ("thunderbolt: Prevent crash if
non-active NVMem file is read").

Add support for write-only nvmem instances by adding attrs for 0200.

Change nvmem_register() to abort if NULL group is returned from
nvmem_sysfs_get_groups().

Return NULL from nvmem_sysfs_get_groups() in invalid cases.

Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
---
drivers/nvmem/core.c | 10 +++++--
drivers/nvmem/nvmem-sysfs.c | 56 +++++++++++++++++++++++++++++++------
2 files changed, 56 insertions(+), 10 deletions(-)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 77d890d3623d..ddc7be5149d5 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -381,6 +381,14 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
nvmem->type = config->type;
nvmem->reg_read = config->reg_read;
nvmem->reg_write = config->reg_write;
+ nvmem->dev.groups = nvmem_sysfs_get_groups(nvmem, config);
+ if (!nvmem->dev.groups) {
+ ida_simple_remove(&nvmem_ida, nvmem->id);
+ gpiod_put(nvmem->wp_gpio);
+ kfree(nvmem);
+ return ERR_PTR(-EINVAL);
+ }
+
if (!config->no_of_node)
nvmem->dev.of_node = config->dev->of_node;

@@ -395,8 +403,6 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
nvmem->read_only = device_property_present(config->dev, "read-only") ||
config->read_only || !nvmem->reg_write;

- nvmem->dev.groups = nvmem_sysfs_get_groups(nvmem, config);
-
device_initialize(&nvmem->dev);

dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);
diff --git a/drivers/nvmem/nvmem-sysfs.c b/drivers/nvmem/nvmem-sysfs.c
index 8759c4470012..9728da948988 100644
--- a/drivers/nvmem/nvmem-sysfs.c
+++ b/drivers/nvmem/nvmem-sysfs.c
@@ -202,16 +202,49 @@ static const struct attribute_group *nvmem_ro_root_dev_groups[] = {
NULL,
};

+/* write only permission, root only */
+static struct bin_attribute bin_attr_wo_root_nvmem = {
+ .attr = {
+ .name = "nvmem",
+ .mode = 0200,
+ },
+ .write = bin_attr_nvmem_write,
+};
+
+static struct bin_attribute *nvmem_bin_wo_root_attributes[] = {
+ &bin_attr_wo_root_nvmem,
+ NULL,
+};
+
+static const struct attribute_group nvmem_bin_wo_root_group = {
+ .bin_attrs = nvmem_bin_wo_root_attributes,
+ .attrs = nvmem_attrs,
+};
+
+static const struct attribute_group *nvmem_wo_root_dev_groups[] = {
+ &nvmem_bin_wo_root_group,
+ NULL,
+};
+
const struct attribute_group **nvmem_sysfs_get_groups(
struct nvmem_device *nvmem,
const struct nvmem_config *config)
{
- if (config->root_only)
- return nvmem->read_only ?
- nvmem_ro_root_dev_groups :
- nvmem_rw_root_dev_groups;
+ /* Read-only */
+ if (nvmem->reg_read && (!nvmem->reg_write || nvmem->read_only))
+ return config->root_only ?
+ nvmem_ro_root_dev_groups : nvmem_ro_dev_groups;
+
+ /* Read-write */
+ if (nvmem->reg_read && nvmem->reg_write && !nvmem->read_only)
+ return config->root_only ?
+ nvmem_rw_root_dev_groups : nvmem_rw_dev_groups;
+
+ /* Write-only, do not honour request for global writable entry */
+ if (!nvmem->reg_read && nvmem->reg_write && !nvmem->read_only)
+ return config->root_only ? nvmem_wo_root_dev_groups : NULL;

- return nvmem->read_only ? nvmem_ro_dev_groups : nvmem_rw_dev_groups;
+ return NULL;
}

/*
@@ -230,17 +263,24 @@ int nvmem_sysfs_setup_compat(struct nvmem_device *nvmem,
if (!config->base_dev)
return -EINVAL;

- if (nvmem->read_only) {
+ if (nvmem->reg_read && (!nvmem->reg_write || nvmem->read_only)) {
if (config->root_only)
nvmem->eeprom = bin_attr_ro_root_nvmem;
else
nvmem->eeprom = bin_attr_ro_nvmem;
- } else {
+ } else if (!nvmem->reg_read && nvmem->reg_write && !nvmem->read_only) {
+ if (config->root_only)
+ nvmem->eeprom = bin_attr_wo_root_nvmem;
+ else
+ return -EINVAL;
+ } else if (nvmem->reg_read && nvmem->reg_write && !nvmem->read_only) {
if (config->root_only)
nvmem->eeprom = bin_attr_rw_root_nvmem;
else
nvmem->eeprom = bin_attr_rw_nvmem;
- }
+ } else
+ return -EINVAL;
+
nvmem->eeprom.attr.name = "eeprom";
nvmem->eeprom.size = nvmem->size;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
--
2.21.0
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