Hi everyone, happy Easter/Passover/Ramadan/perfectly-normal-Sunday/etc! I'm trying to get this project (https://github.com/TriForceX/MiyooCFW) to a point where we can build the entire thing from source and have it actually work. The piece I'm stuck on right now is the video driver - if I use a pre-compiled u-boot then linux can boot and display a picture, but if I build u-boot from source, then I can't get any picture. (I know linux booted, because one of the initial programs plays a "bing" sound and I can hear that. Also, I can make it write logs to a file on the microsd.)
My assumption is that the pre-compiled u-boot is doing some setup that mine isn't, and the Linux video driver is (inadvertently?) depending on this setup. I'd like to figure out what this setup is and make the Linux driver capable of doing it if necessary. I'm certain that the u-boot source code the project has isn't what was used to build the pre-compiled binary because, in addition to the linux video issues, the u-boot splash logo is different. (Oh, and I had to set CONFIG_VIDEO_SUNXI=y to get it to show any splash logo.) Worth mentioning, the video driver supports 4 different panel ICs, mine is version 2, which uses a ST7789S. I did some work towards documenting it here: https://github.com/MiyooCFW/kernel/pull/12/files I've spent some time reading the source of the u-boot <https://github.com/MiyooCFW/uboot/blob/master/drivers/video/sunxi/sunxi_display.c> and linux video drivers <https://github.com/MiyooCFW/kernel/blob/master/drivers/video/fbdev/r61520fb.c>, trying to spot the differences, but I haven't yet figured out which differences are relevant. I did notice that the u-boot one just draws a single hard-coded image <https://github.com/MiyooCFW/uboot/blob/2b7c43e6499409ec6accd8fbd73996b42d922bac/drivers/video/sunxi/sunxi_display.c#L1727-L1748> and nothing else, which seems.. less than ideal. I've tried comparing various bits of memory with printk after booting from one u-boot or the other. (For these comparisons, I left CONFIG_VIDEO_SUNXI unset in my u-boot build): * the result of readl(iomm.lcdc + TCON_CLK_CTRL_REG) <https://github.com/MiyooCFW/kernel/blob/9d69b562d8dc252a93af80e399069312e89e2184/drivers/video/fbdev/r61520fb.c#L1117> is - with pre-compiled u-boot: `0xF0000006` - with u-boot from source: `0` * after sending command `0x04` to identify the panel IC <https://github.com/MiyooCFW/kernel/blob/9d69b562d8dc252a93af80e399069312e89e2184/drivers/video/fbdev/r61520fb.c#L406>, the response (4 calls to `lcdc_rd_dat()`) is - with pre-compiled u-boot: `0`, `0`, `0x85`, `0x85` - with u-boot from source: `0`, `0`, `0`, `0` Correcting the TCON_CLK_CTRL_REG and ignoring the identity check and instead forcing the panel to v2 are not enough to get video working. There are probably some other differences that I haven't found yet. I spent a lot of time reading through the documentation and source that was provided by one of the manufacturers <https://drive.google.com/drive/folders/1PAYQC8loV2114ips-0wjMxzbXa4VdLp5>. I haven't finished yet, but so far nothing has jumped out at me as "this is the fix you need". I also tried comparing the two u-boot bins with Ghidra's Version Tracking tool to try and identify the differences, but I got kind of overwhelmed and wasn't able to figure anything out. (I'd only ever used ghidra once before.) I also found source code for a previous release <https://github.com/steward-fu/miyoo/releases>, but hit errors when trying to compile it. I didn't go much farther down that route. I think I could go farther down each of these routes, but I'm not sure which one makes the most sense to put more effort into. I suspect that the change I need is fairly small, and perhaps even obvious to someone who knows more about this stuff, but I kind of feel like I'm just banging my head into a wall and not getting anywhere. So, do you all have any advice for me? Thanks, -Nathan -- You received this message because you are subscribed to the Google Groups "linux-sunxi" group. To unsubscribe from this group and stop receiving emails from it, send an email to linux-sunxi+unsubscr...@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/linux-sunxi/6ed50086-7029-4b61-8ecb-d51741911577n%40googlegroups.com.
