linux-kernel - Re: [RFC PATCH 2/3] drivers: misc: eeprom: at24: support reading mac eeprom from different addresses

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Message-ID: <b67a323b-5562-1259-08f1-fa7ee3509e8b@lechnology.com>
Date:   Thu, 29 Jun 2017 10:32:12 -0500
From:   David Lechner <david@...hnology.com>
To:     Claudiu Beznea <claudiu.beznea@...rochip.com>, robh+dt@...nel.org,
        mark.rutland@....com, nsekhar@...com, wsa@...-dreams.de
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-i2c@...r.kernel.org, nicolas.ferre@...rochip.com
Subject: Re: [RFC PATCH 2/3] drivers: misc: eeprom: at24: support reading mac
 eeprom from different addresses

On 06/29/2017 06:39 AM, Claudiu Beznea wrote:
> Add support for reading from different offsets of EEPROM.
> The offset is initialized via device tree. If nothing is
> given as input the old value, 0x90, is used. In this way
> the driver could be used as generic driver for different
> vendor memories by only changing the reading offset via
> device tree.
> 
> Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
> ---
>   drivers/misc/eeprom/at24.c         | 5 ++++-
>   include/linux/platform_data/at24.h | 1 +
>   2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
> index 764ff5df..53c5fb8 100644
> --- a/drivers/misc/eeprom/at24.c
> +++ b/drivers/misc/eeprom/at24.c
> @@ -365,7 +365,7 @@ static ssize_t at24_eeprom_read_mac(struct at24_data *at24, char *buf,
>   	memset(msg, 0, sizeof(msg));
>   	msg[0].addr = client->addr;
>   	msg[0].buf = addrbuf;
> -	addrbuf[0] = 0x90 + offset;
> +	addrbuf[0] = at24->chip.offset + offset;
>   	msg[0].len = 1;
>   	msg[1].addr = client->addr;
>   	msg[1].flags = I2C_M_RD;
> @@ -581,6 +581,9 @@ static void at24_get_pdata(struct device *dev, struct at24_platform_data *chip)
>   		 */
>   		chip->page_size = 1;
>   	}
> +	err = device_property_read_u8(dev, "start-offset", &chip->offset);

Why use u8 here? I have an at24 EEPROM that uses 16-bit addressing where 
the MAC address is stored at 0x3F06. Seems like it would be better to 
just use u32, then you don't have to mess with /bits/ in the device tree 
binding.

> +	if (err)
> +		chip->offset = 0x90;
>   }
>   
>   static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
> diff --git a/include/linux/platform_data/at24.h b/include/linux/platform_data/at24.h
> index 271a4e2..d55c454 100644
> --- a/include/linux/platform_data/at24.h
> +++ b/include/linux/platform_data/at24.h
> @@ -50,6 +50,7 @@ struct at24_platform_data {
>   #define AT24_FLAG_TAKE8ADDR	BIT(4)	/* take always 8 addresses (24c00) */
>   #define AT24_FLAG_SERIAL	BIT(3)	/* factory-programmed serial number */
>   #define AT24_FLAG_MAC		BIT(2)	/* factory-programmed mac address */
> +	u8		offset;
>   
>   	void		(*setup)(struct nvmem_device *nvmem, void *context);
>   	void		*context;
>