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Message-ID: <0affe06b-08ad-aadf-c936-2c93b5e2b904@linaro.org>
Date: Thu, 13 Jul 2023 10:16:46 +0100
From: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To: Miquel Raynal <miquel.raynal@...tlin.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org
Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
Robert Marko <robert.marko@...tura.hr>,
Luka Perkov <luka.perkov@...tura.hr>
Subject: Re: [PATCH RESEND v5 2/2] nvmem: core: Expose cells through sysfs
This one seems to be an extra patch in the series :-)
On 13/07/2023 08:55, Miquel Raynal wrote:
> The binary content of nvmem devices is available to the user so in the
> easiest cases, finding the content of a cell is rather easy as it is
> just a matter of looking at a known and fixed offset. However, nvmem
> layouts have been recently introduced to cope with more advanced
> situations, where the offset and size of the cells is not known in
> advance or is dynamic. When using layouts, more advanced parsers are
> used by the kernel in order to give direct access to the content of each
> cell, regardless of its position/size in the underlying
> device. Unfortunately, these information are not accessible by users,
> unless by fully re-implementing the parser logic in userland.
>
> Let's expose the cells and their content through sysfs to avoid these
> situations. Of course the relevant NVMEM sysfs Kconfig option must be
> enabled for this support to be available.
>
> Not all nvmem devices expose cells. Indeed, the .bin_attrs attribute
> group member will be filled at runtime only when relevant and will
> remain empty otherwise. In this case, as the cells attribute group will
> be empty, it will not lead to any additional folder/file creation.
>
> Exposed cells are read-only. There is, in practice, everything in the
> core to support a write path, but as I don't see any need for that, I
> prefer to keep the interface simple (and probably safer). The interface
> is documented as being in the "testing" state which means we can later
> add a write attribute if though relevant.
>
> There is one limitation though: if a layout is built as a module but is
> not properly installed in the system and loaded manually with insmod
> while the nvmem device driver was built-in, the cells won't appear in
> sysfs. But if done like that, the cells won't be usable by the built-in
> kernel drivers anyway.
>
> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
> drivers/nvmem/core.c | 121 ++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 113 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 3f8c7718412b..8b49b12501e2 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -325,6 +325,43 @@ static umode_t nvmem_bin_attr_is_visible(struct kobject *kobj,
> return nvmem_bin_attr_get_umode(nvmem);
> }
>
> +static struct nvmem_cell *nvmem_create_cell(struct nvmem_cell_entry *entry,
> + const char *id, int index);
> +
> +static ssize_t nvmem_cell_attr_read(struct file *filp, struct kobject *kobj,
> + struct bin_attribute *attr, char *buf,
> + loff_t pos, size_t count)
> +{
> + struct nvmem_cell_entry *entry;
> + struct nvmem_cell *cell = NULL;
> + size_t cell_sz, read_len;
> + void *content;
> +
> + entry = attr->private;
> + cell = nvmem_create_cell(entry, entry->name, 0);
> + if (IS_ERR(cell))
> + return PTR_ERR(cell);
> +
> + if (!cell)
> + return -EINVAL;
> +
> + content = nvmem_cell_read(cell, &cell_sz);
> + if (IS_ERR(content)) {
> + read_len = PTR_ERR(content);
> + goto destroy_cell;
> + }
> +
> + read_len = min_t(unsigned int, cell_sz - pos, count);
> + memcpy(buf, content + pos, read_len);
> + kfree(content);
> +
> +destroy_cell:
> + kfree_const(cell->id);
> + kfree(cell);
> +
> + return read_len;
> +}
> +
> /* default read/write permissions */
> static struct bin_attribute bin_attr_rw_nvmem = {
> .attr = {
> @@ -346,8 +383,14 @@ static const struct attribute_group nvmem_bin_group = {
> .is_bin_visible = nvmem_bin_attr_is_visible,
> };
>
> +/* Cell attributes will be dynamically allocated */
> +static struct attribute_group nvmem_cells_group = {
> + .name = "cells",
> +};
> +
> static const struct attribute_group *nvmem_dev_groups[] = {
> &nvmem_bin_group,
> + &nvmem_cells_group,
> NULL,
> };
>
> @@ -406,6 +449,58 @@ static void nvmem_sysfs_remove_compat(struct nvmem_device *nvmem,
> device_remove_bin_file(nvmem->base_dev, &nvmem->eeprom);
> }
>
> +static int nvmem_populate_sysfs_cells(struct nvmem_device *nvmem)
> +{
> + struct bin_attribute **cells_attrs, *attrs;
> + struct nvmem_cell_entry *entry;
> + unsigned int ncells = 0, i = 0;
> + int ret = 0;
> +
> + mutex_lock(&nvmem_mutex);
> +
> + if (list_empty(&nvmem->cells))
> + goto unlock_mutex;
> +
> + /* Allocate an array of attributes with a sentinel */
> + ncells = list_count_nodes(&nvmem->cells);
> + cells_attrs = devm_kcalloc(&nvmem->dev, ncells + 1,
> + sizeof(struct bin_attribute *), GFP_KERNEL);
> + if (!cells_attrs) {
> + ret = -ENOMEM;
> + goto unlock_mutex;
> + }
> +
> + attrs = devm_kcalloc(&nvmem->dev, ncells, sizeof(struct bin_attribute), GFP_KERNEL);
> + if (!attrs) {
> + ret = -ENOMEM;
> + goto unlock_mutex;
> + }
> +
> + /* Initialize each attribute to take the name and size of the cell */
> + list_for_each_entry(entry, &nvmem->cells, node) {
> + sysfs_bin_attr_init(&attrs[i]);
> + attrs[i].attr.name = devm_kstrdup(&nvmem->dev, entry->name, GFP_KERNEL);
> + attrs[i].attr.mode = 0444;
> + attrs[i].size = entry->bytes;
> + attrs[i].read = &nvmem_cell_attr_read;
> + attrs[i].private = entry;
> + if (!attrs[i].attr.name) {
> + ret = -ENOMEM;
> + goto unlock_mutex;
> + }
> +
> + cells_attrs[i] = &attrs[i];
> + i++;
> + }
> +
> + nvmem_cells_group.bin_attrs = cells_attrs;
> +
> +unlock_mutex:
> + mutex_unlock(&nvmem_mutex);
> +
> + return ret;
> +}
> +
> #else /* CONFIG_NVMEM_SYSFS */
>
> static int nvmem_sysfs_setup_compat(struct nvmem_device *nvmem,
> @@ -998,20 +1093,30 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> if (rval)
> goto err_remove_cells;
>
> + rval = nvmem_add_cells_from_layout(nvmem);
> + if (rval)
> + goto err_remove_cells;
> +
> + rval = nvmem_add_cells_from_fixed_layout(nvmem);
> + if (rval)
> + goto err_remove_cells;
> +
> + rval = nvmem_add_cells_from_layout(nvmem);
> + if (rval)
> + goto err_remove_cells;
> +
> +#ifdef CONFIG_NVMEM_SYSFS
> + rval = nvmem_populate_sysfs_cells(nvmem);
> + if (rval)
> + goto err_remove_cells;
> +#endif
> +
> dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);
>
> rval = device_add(&nvmem->dev);
> if (rval)
> goto err_remove_cells;
>
> - rval = nvmem_add_cells_from_fixed_layout(nvmem);
> - if (rval)
> - goto err_remove_cells;
> -
> - rval = nvmem_add_cells_from_layout(nvmem);
> - if (rval)
> - goto err_remove_cells;
> -
> blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);
>
> return nvmem;
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