Hi all, I have a design problem I'm not sure how to solve cleanly. I have a board using a PTN3460 eDP => LVDS bridge and a LP8556 backlight controller. Both of these are already supported by the kernel. The PTN3460 has an electrical output signal (PVCGEN) that is intended to control power to the panel and goes high once valid video data is received on the eDP link. However on this board this signal actually switches the power to the LP8556. The consequences of this are * Until the video link is up it is not possible to communicate with the LP8556 over I2C (indeed the driver fails to probe due to this) * If the video link goes down the LP8556 loses all its state The LP8556 can either control the backlight via I2C or by an external PWM input signal (which is connected to the PTN3460) So I could *mostly* solve the problem of getting a backlight control by not using I2C communication with the LP8556 and controlling the backlight using the PWM. Currently the PTN3460 driver does not implement PWM control but it would be fairly easy to add and there is already a precedent in the parade-ps8622 driver that implements a backlight control. However that does not solve the I2C communications issue, just avoids the need for it for setting the backlight brightness. So if I need to do other things with the LP8556 (like tuning the drive strengths etc it's back to the same problem). What seems to be needed is a way of expressing that the PTN3460 supplies power to the LP8556 but the LP8556 does not control it. A normal regulator relationship doesn't work because there it is expected that the consumer (LP8556) controls the regulator. Any ideas appreciated. Martin
