alexfreed58 Posted April 20, 2021 Posted April 20, 2021 (edited) Hi, I realize that V3s is not H2 or H3, but I hope the question is generic. Is it possible to make the FB 16 bit? In mainline Linux? I'm working with a Lichee Pi board. The depth is 18 bits but the fb in Linux is 32 bit. I'd love to get it down to 16 bits to save 1/2 of the video memory and just 2 color bits are a small price to pay. I understand that Linux inherits the FB from u-boot. Edited April 20, 2021 by alexfreed58
Werner Posted April 20, 2021 Posted April 20, 2021 Moved to Common issues / peer to peer technical support
jernej Posted April 20, 2021 Posted April 20, 2021 7 hours ago, alexfreed58 said: I understand that Linux inherits the FB from u-boot. That may or may not be true. Linux has proper V3s display driver for a long time. However, U-Boot may still hand over its FB to Linux. In that case U-Boot FB is used for a very short time and it's replaced with Linux FB during boot. Now, I'm not sure if U-Boot FB memory is actually released or just stays reserved. Best way to check would be to disable display driver in U-Boot (via U-Boot config and rebuild) and compare free memory. I don't know how to force 16-bit buffer. There is probably some kind of kernel parameter for that.
alexfreed58 Posted April 20, 2021 Author Posted April 20, 2021 I have built u-boot with different parameters in the .config file for several LCD panels: 800x480 and 800x600. That becomes the size of the reported uboot screen and also the Linux kernel inherits the same size. But always 32 bit, even if I put the depth=16 rather than the standard depth=18 into the configuration. My problem is not with the memory allocated internally for the FB: it's the application in the user space that needs many off the screen windows (pixel buffers, really) that have to match the ARGB FB format. Anybody?
jernej Posted April 20, 2021 Posted April 20, 2021 Ah, you didn't add panel description to DT for Linux. So yes, Linux uses U-Boot FB. 32-bit colours are hardcoded in U-Boot here: https://source.denx.de/u-boot/u-boot/-/blob/master/drivers/video/sunxi/sunxi_de2.c#L255 Fortunately for you, I added handling 16-bit colours (if you change constant), but I can't guarantee it will work. I only tested it in U-Boot for H3 and not in Linux. EDIT: Apparently you have to change also this line: https://source.denx.de/u-boot/u-boot/-/blob/master/drivers/video/sunxi/sunxi_de2.c#L405
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