Re: [PATCH v3 02/11] media: ov772x: allow i2c controllers without I2C_FUNC_PROTOCOL_MANGLING

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Mita-san,

On Sunday, 22 April 2018 18:56:08 EEST Akinobu Mita wrote:
> The ov772x driver only works when the i2c controller have
> I2C_FUNC_PROTOCOL_MANGLING.  However, many i2c controller drivers don't
> support it.
> 
> The reason that the ov772x requires I2C_FUNC_PROTOCOL_MANGLING is that
> it doesn't support repeated starts.
> 
> This changes the reading ov772x register method so that it doesn't
> require I2C_FUNC_PROTOCOL_MANGLING by calling two separated i2c messages.

As commented in a reply to v1, given that this implementation is in no way 
specific to the ov772x driver, I'd prefer implementing the fallback in the I2C 
core instead.

> Cc: Jacopo Mondi <jacopo+renesas@jmondi.org>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: Hans Verkuil <hans.verkuil@cisco.com>
> Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
> Cc: Mauro Carvalho Chehab <mchehab@s-opensource.com>
> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> ---
> * v3
> - Remove I2C_CLIENT_SCCB flag set as it isn't needed anymore
> 
>  drivers/media/i2c/ov772x.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/media/i2c/ov772x.c b/drivers/media/i2c/ov772x.c
> index b62860c..2ae730f 100644
> --- a/drivers/media/i2c/ov772x.c
> +++ b/drivers/media/i2c/ov772x.c
> @@ -542,9 +542,19 @@ static struct ov772x_priv *to_ov772x(struct v4l2_subdev
> *sd) return container_of(sd, struct ov772x_priv, subdev);
>  }
> 
> -static inline int ov772x_read(struct i2c_client *client, u8 addr)
> +static int ov772x_read(struct i2c_client *client, u8 addr)
>  {
> -	return i2c_smbus_read_byte_data(client, addr);
> +	int ret;
> +	u8 val;
> +
> +	ret = i2c_master_send(client, &addr, 1);
> +	if (ret < 0)
> +		return ret;
> +	ret = i2c_master_recv(client, &val, 1);
> +	if (ret < 0)
> +		return ret;
> +
> +	return val;
>  }
> 
>  static inline int ov772x_write(struct i2c_client *client, u8 addr, u8
> value) @@ -1255,13 +1265,11 @@ static int ov772x_probe(struct i2c_client
> *client, return -EINVAL;
>  	}
> 
> -	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA |
> -					      I2C_FUNC_PROTOCOL_MANGLING)) {
> +	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA)) {
>  		dev_err(&adapter->dev,
> -			"I2C-Adapter doesn't support SMBUS_BYTE_DATA or PROTOCOL_MANGLING
\n");
> +			"I2C-Adapter doesn't support SMBUS_BYTE_DATA\n");
>  		return -EIO;
>  	}
> -	client->flags |= I2C_CLIENT_SCCB;
> 
>  	priv = devm_kzalloc(&client->dev, sizeof(*priv), GFP_KERNEL);
>  	if (!priv)


-- 
Regards,

Laurent Pinchart