Re: [PATCH 1/6 v4] media: V4L2: support asynchronous subdevice registration

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

Hi Sylwester,

On Tuesday 08 January 2013 12:37:36 Sylwester Nawrocki wrote:
> On 01/08/2013 11:35 AM, Laurent Pinchart wrote:
> >>>>> If we need a workaround, I'd rather pass the device name in addition
> >>>>> to the I2C adapter number and address, instead of embedding the
> >>>>> workaround in this new API.
> >>>> 
> >>>> ...or we can change the I2C subdevice name format. The actual need to
> >>>> do
> >>>> 
> >>>> 	snprintf(clk_name, sizeof(clk_name), "%s %d-%04x",
> >>>> 		 asdl->dev->driver->name,
> >>>> 		 i2c_adapter_id(client->adapter), client->addr);
> >>>> 
> >>>> in soc-camera now to exactly match the subdevice name, as created by
> >>>> v4l2_i2c_subdev_init(), doesn't make me specifically happy either. What
> >>>> if the latter changes at some point? Or what if one driver wishes to
> >>>> create several subdevices for one I2C device?
> >>> 
> >>> The common clock framework uses %d-%04x, maybe we could use that as well
> >>> for clock names ?
> >> 
> >> And preserve the subdevice names? Then matching would be more difficult
> >> and less precise. Or change subdevice names too? I think, we can do the
> >> latter, since anyway at any time only one driver can be attached to an
> >> I2C device.
> > 
> > That's right. Where else is the subdev name used ?
> 
> Subdev names are exposed to user space by the media controller API.
> So they are really part of an ABI, aren't they ?

They're used to construct the name exposed to userspace, but the media 
controller core could probably handle that internally by concatenating the 
driver name and the subdev name.

> Also having I2C bus number or I2C slave address as part of the subdev
> name makes it more difficult to write portable applications. Hence
> in sensor drivers I used to overwrite subdev name to remove I2C bus
> and slave address, as the format used v4l2_i2c_subdev_init() seemed
> highly unsuitable..

This clearly shows that we need to discuss the matter and agree on a common 
mode of operation.

Aren't applications that use the subdev name directly inherently non-portable 
anyway ? If you want your application to support different boards/sensors/SoCs 
you should discover the pipeline and find the sensor by iterating over 
entities, instead of using the sensor entity name.

-- 
Regards,

Laurent Pinchart