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

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2018-04-09 15:58 GMT+09:00 jacopo mondi <jacopo@xxxxxxxxxx>:
> Hello Akinobu,
>     thank you for the patch.
>
> On which platform have you tested the series (just curious) ?

I use Zynq-7000 development board with Xilinx Video IP driver and
custom video pipeline design based on the example reference project.

> 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.

I'll replace the read() function to the new implementation in the next
version of this patchset. Although handling in the I2C core is fascinating,
I feel the area of influence is a bit large.

> 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@xxxxxxxxxx>
>> Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
>> Cc: Hans Verkuil <hans.verkuil@xxxxxxxxx>
>> Cc: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
>> Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>
>> Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
>> ---
>>  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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