It seems that we have no more issues with LCD and backlight management. LCD switches on/off flawlessly, so does LCD backlight :)
I've just fixed a problem with backlight not enabling after it was disabled. I've discussed PWM-problems with my friend Ordog (it's his nickname), and he suggested to play with PWM frequency; he described how it can work, and proposed some reasons why it doesn't enable in my case. I decided that backlight needs wormup to switch on properly, I've checked this hypothesis - and it works! Backlight switches on properly after short "warmup". So, thanks to Ordog!
Yesterday I've submited my patchset to the linux-arm-kernel maillist. I still have no response about rx1950-related patches, but s3c2440-udc related patch brought up small discussion. You can read it on linux-arm-kernel maillist archive if you're interested in it :)