linux-kernel - Re: [PATCH v12 7/7] nvmem: core: Expose cells through sysfs

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Date:   Mon, 9 Oct 2023 10:48:17 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Michael Walle <michael@...le.cc>,
        Rafał Miłecki <rafal@...ecki.pl>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Robert Marko <robert.marko@...tura.hr>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Luka Perkov <luka.perkov@...tura.hr>,
        Randy Dunlap <rdunlap@...radead.org>,
        Chen-Yu Tsai <wenst@...omium.org>,
        Daniel Golle <daniel@...rotopia.org>
Subject: Re: [PATCH v12 7/7] nvmem: core: Expose cells through sysfs



On 05/10/2023 16:59, Miquel Raynal wrote:
> , 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	= {
> @@ -320,11 +357,21 @@ 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,
>   	NULL,
>   };
>   
> +static const struct attribute_group *nvmem_cells_groups[] = {
> +	&nvmem_cells_group,
> +	NULL,
> +};
> +
>   static struct bin_attribute bin_attr_nvmem_eeprom_compat = {
>   	.attr	= {
>   		.name	= "eeprom",
> @@ -380,6 +427,68 @@ 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) || nvmem->sysfs_cells_populated) {
> +		nvmem_cells_group.bin_attrs = NULL;
> +		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_kasprintf(&nvmem->dev, GFP_KERNEL,
> +						    "%s@%x", entry->name,
> +						    entry->offset);
> +		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;
> +
> +	ret = devm_device_add_groups(&nvmem->dev, nvmem_cells_groups);
> +	if (ret)
> +		goto unlock_mutex;

This is going to create groups after the nvmem device is added, isn't 
this going to be problem with user space notifications?

--srini
> +
> +	nvmem->sysfs_cells_populated = true;
> +
> +unlock_mutex:
> +	mutex_unlock(&nvmem_mutex);
> +
> +	return ret;