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Date: Fri, 12 Apr 2024 11:43:19 +0200
From: Marco Felsch <m.felsch@pengutronix.de>
To: srinivas.kandagatla@linaro.org, miquel.raynal@bootlin.com,
	michael@walle.cc
Cc: linux-kernel@vger.kernel.org, kernel@pengutronix.de
Subject: Re: [PATCH] nvmem: core: add sysfs cell write support
Message-ID: <20240412094319.ua3galjwe6bwnavf@pengutronix.de>
References: <20240223154129.1902905-1-m.felsch@pengutronix.de>
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In-Reply-To: <20240223154129.1902905-1-m.felsch@pengutronix.de>

Hi,

gentle ping.

Regards,
  Marco

On 24-02-23, Marco Felsch wrote:
> Add the sysfs cell write support to make it possible to write to exposed
> cells from sysfs as well e.g. for device provisioning. The write support
> is limited to EEPROM based nvmem devices and to nvmem-cells which don't
> require post-processing.
> 
> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> ---
>  drivers/nvmem/core.c | 43 ++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 42 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 980123fb4dde..b1f86cb431ef 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -336,6 +336,40 @@ static ssize_t nvmem_cell_attr_read(struct file *filp, struct kobject *kobj,
>  	return read_len;
>  }
>  
> +static ssize_t nvmem_cell_attr_write(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;
> +	int ret;
> +
> +	entry = attr->private;
> +
> +	if (!entry->nvmem->reg_write)
> +		return -EPERM;
> +
> +	if (pos >= entry->bytes)
> +		return -EFBIG;
> +
> +	if (pos + count > entry->bytes)
> +		count = entry->bytes - pos;
> +
> +	cell = nvmem_create_cell(entry, entry->name, 0);
> +	if (IS_ERR(cell))
> +		return PTR_ERR(cell);
> +
> +	if (!cell)
> +		return -EINVAL;
> +
> +	ret = nvmem_cell_write(cell, buf, count);
> +
> +	kfree_const(cell->id);
> +	kfree(cell);
> +
> +	return ret;
> +}
> +
>  /* default read/write permissions */
>  static struct bin_attribute bin_attr_rw_nvmem = {
>  	.attr	= {
> @@ -458,13 +492,20 @@ static int nvmem_populate_sysfs_cells(struct nvmem_device *nvmem)
>  
>  	/* Initialize each attribute to take the name and size of the cell */
>  	list_for_each_entry(entry, &nvmem->cells, node) {
> +		umode_t mode = nvmem_bin_attr_get_umode(nvmem);
> +
> +		/* Limit cell-write support to EEPROMs at the moment */
> +		if (entry->read_post_process || nvmem->type != NVMEM_TYPE_EEPROM)
> +			mode &= ~0222;
> +
>  		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].attr.mode = mode;
>  		attrs[i].size = entry->bytes;
>  		attrs[i].read = &nvmem_cell_attr_read;
> +		attrs[i].write = &nvmem_cell_attr_write;
>  		attrs[i].private = entry;
>  		if (!attrs[i].attr.name) {
>  			ret = -ENOMEM;
> -- 
> 2.39.2
> 
> 
>