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

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

Hi Mita-san,

(CC'ing Wolfram Sang)

On Monday, 23 April 2018 18:55:20 EEST Akinobu Mita wrote:
> 2018-04-23 18:18 GMT+09:00 Laurent Pinchart:
> > 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.
> 
> Do you have any ideas how to implement in the I2C core?
> I wonder if I can modify i2c_smbus_read_byte_data() or i2c_transfer()
> for I2C_CLIENT_SCCB.

How about i2c_smbus_xfer_emulated() ? The tricky part will be to handle the 
I2C adapters that implement .smbus_xfer(), as those won't go through 
i2c_smbus_xfer_emulated(). i2c_smbus_xfer_emulated() relies on i2c_transfer(), 
which itself relies on the I2C adapter's .master_xfer() operation. We're thus 
only concerned about the drivers that implement both .smbus_xfer() and 
master_xfer(), and there's only 4 of them (i2c-opal, i2c-pasemi, i2c-powermac 
and i2c-zx2967). Maybe the simplest solution would be to force the emulation 
path if I2C_CLIENT_SCCB && !I2C_FUNC_PROTOCOL_MANGLING && ->master_xfer != 
NULL ?

Wolfram, what do you think ?

> >> 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