Re: [PATCH 1/6] media: ov772x: allow i2c controllers without I2C_FUNC_PROTOCOL_MANGLING

[jacopo mondi <jacopo@jmondi.org>]

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Hello Akinobu,
    thank you for the patch.

On which platform have you tested the series (just curious) ?

On Sun, Apr 08, 2018 at 12:48:05AM +0900, 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 change adds an alternative method for reading from ov772x register
> which uses two separated i2c messages for the i2c controllers without
> I2C_FUNC_PROTOCOL_MANGLING.

Actually, and please correct me if I'm wrong, what I see here is that
an i2c_master_send+i2c_master_recv sequence is equivalent to a mangled
smbus transaction:

i2c_smbus_read_byte_data | I2C_CLIENT_SCCB:
S Addr Wr [A] Comm [A] P S Addr Rd [A] [Data] NA P

i2c_master_send() + i2c_master_recv():
S Addr Wr [A] Data [A] P
S Addr Rd [A] [Data] NA P

I wonder if it is not worth to ditch the existing read() function in
favour of your new proposed one completely.

I have tested it on the Migo-R board where I have an ov772x installed
and it works fine.

Although I would like to have a confirmation this is fine by people
how has seen more i2c adapters in action than me :)

Thanks
   j

>
> 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>
> ---
>  drivers/media/i2c/ov772x.c | 42 +++++++++++++++++++++++++++++++++---------
>  1 file changed, 33 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/media/i2c/ov772x.c b/drivers/media/i2c/ov772x.c
> index b62860c..283ae2c 100644
> --- a/drivers/media/i2c/ov772x.c
> +++ b/drivers/media/i2c/ov772x.c
> @@ -424,6 +424,7 @@ struct ov772x_priv {
>  	/* band_filter = COM8[5] ? 256 - BDBASE : 0 */
>  	unsigned short                    band_filter;
>  	unsigned int			  fps;
> +	int (*reg_read)(struct i2c_client *client, u8 addr);
>  };
>
>  /*
> @@ -542,11 +543,34 @@ 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)
> +{
> +	struct v4l2_subdev *sd = i2c_get_clientdata(client);
> +	struct ov772x_priv *priv = to_ov772x(sd);
> +
> +	return priv->reg_read(client, addr);
> +}
> +
> +static int ov772x_reg_read(struct i2c_client *client, u8 addr)
>  {
>  	return i2c_smbus_read_byte_data(client, addr);
>  }
>
> +static int ov772x_reg_read_fallback(struct i2c_client *client, u8 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)
>  {
>  	return i2c_smbus_write_byte_data(client, addr, value);
> @@ -1255,20 +1279,20 @@ static int ov772x_probe(struct i2c_client *client,
>  		return -EINVAL;
>  	}
>
> -	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA |
> -					      I2C_FUNC_PROTOCOL_MANGLING)) {
> -		dev_err(&adapter->dev,
> -			"I2C-Adapter doesn't support SMBUS_BYTE_DATA or PROTOCOL_MANGLING\n");
> -		return -EIO;
> -	}
> -	client->flags |= I2C_CLIENT_SCCB;
> -
>  	priv = devm_kzalloc(&client->dev, sizeof(*priv), GFP_KERNEL);
>  	if (!priv)
>  		return -ENOMEM;
>
>  	priv->info = client->dev.platform_data;
>
> +	if (i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA |
> +					     I2C_FUNC_PROTOCOL_MANGLING))
> +		priv->reg_read = ov772x_reg_read;
> +	else
> +		priv->reg_read = ov772x_reg_read_fallback;
> +
> +	client->flags |= I2C_CLIENT_SCCB;
> +
>  	v4l2_i2c_subdev_init(&priv->subdev, client, &ov772x_subdev_ops);
>  	v4l2_ctrl_handler_init(&priv->hdl, 3);
>  	v4l2_ctrl_new_std(&priv->hdl, &ov772x_ctrl_ops,
> --
> 2.7.4
>

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