linux-kernel - Re: [RFC PATCH net-next 9/9] ethtool: Add ability to flash transceiver modules' firmware

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Message-ID: <Za/pBGBB3H+VEbX8@shell.armlinux.org.uk>
Date: Tue, 23 Jan 2024 16:27:48 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Danielle Ratson <danieller@...dia.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, corbet@....net, sdf@...gle.com,
	kory.maincent@...tlin.com, maxime.chevallier@...tlin.com,
	vladimir.oltean@....com, przemyslaw.kitszel@...el.com,
	ahmed.zaki@...el.com, richardcochran@...il.com, shayagr@...zon.com,
	paul.greenwalt@...el.com, jiri@...nulli.us,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	mlxsw@...dia.com, petrm@...dia.com, idosch@...dia.com
Subject: Re: [RFC PATCH net-next 9/9] ethtool: Add ability to flash
 transceiver modules' firmware

On Mon, Jan 22, 2024 at 10:45:30AM +0200, Danielle Ratson wrote:
> +#define MODULE_EEPROM_PAGE	0
> +#define MODULE_EEPROM_OFFSET	0
> +#define MODULE_EEPROM_LENGTH	1
> +#define MODULE_EEPROM_I2C_ADDR	0x50
> +
> +static int module_flash_fw_work_init(struct ethtool_module_fw_flash *module_fw,
> +				     struct net_device *dev,
> +				     struct netlink_ext_ack *extack)
> +{
> +	const struct ethtool_ops *ops = dev->ethtool_ops;
> +	struct ethtool_module_eeprom page_data = {};
> +	struct module_sff8024_id_rpl *rpl;
> +	int err;
> +
> +	/* Fetch the SFF-8024 Identifier Value. For all supported standards, it
> +	 * is located at I2C address 0x50, byte 0. See section 4.1 in SFF-8024,
> +	 * revision 4.9.
> +	 */
> +	page_data.page = MODULE_EEPROM_PAGE;
> +	page_data.offset = MODULE_EEPROM_OFFSET;
> +	page_data.length = MODULE_EEPROM_LENGTH;
> +	page_data.i2c_address = MODULE_EEPROM_I2C_ADDR;

Please use better names - these aren't any better than using integers.

Maybe use SFP_PHYS_ID for the offset?

> +	page_data.data = kmalloc(page_data.length, GFP_KERNEL);
> +	if (!page_data.data)
> +		return -ENOMEM;
> +
> +	err = ops->get_module_eeprom_by_page(dev, &page_data, extack);
> +	if (err < 0)
> +		goto out;
> +
> +	rpl = (struct module_sff8024_id_rpl *)page_data.data;

What purpose does this structure of a single byte serve? To me, it just
obfuscates the code.

	u8 phys_id;

	...
	page_data.offset = SFP_PHYS_ID;
	page_data.length = sizeof(phys_id);
	page_data.data = &phys_id;
	...
	switch (phys_id) {

will work just as well, and be more explicit about what's actually going
on here. It doesn't mean that I have to understand what this new
module_sff8024_id_rpl structure is. I can see that we're just getting
one byte which is the module physical ID.

You also then don't need to care about kfree()ing one byte of data
structure.

-- 
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