Saturday, March 21. 2009, 10:21 AM
The first step of the soc-camera framework conversion to the v4l2-device API is the transformation of the soc-camera core driver to a platform driver. This way the bond between soc-camera and single (sensor, decoder,...) I2C device drivers is becoming weaker and the double probing of those I2C drivers is eliminated.
The reason for the double probing previously has been, that many camera sensors have their I2C interfaces disabled in the absence of the master clock. Therefore the actual I2C probing routine could not access the chip and only registered the device with the soc-camera framework and reported success unconditionally. Then, when the soc-camera framework found a match between a camera device and a host, it registered respective devices and the second stage probing has been initiated, which switched the master clock of the camera interface on and made the actual I2C probing possible.
With the new platform-device approach first soc-camera core probe method is called, which switches the master clock on, and when the camera device driver becomes available, its I2C probe method is called and it can immediately access device I2C registers and perform the actual device identification and initialisation.
The first part of this conversion has been to convert a specific configuration to this scheme. The chosen configuration is the i.MX31 host and a MT9T031 camera, which have been successfully converted and an RFC patch has been posted to the V4L mailing list.
