Cyclone V Frame Buffer II - problem with device Tree and with understanding the address map

Hi, I’m trying to display something via VGA on linux system without desktop (the final goal is to launch Qt app writing to /dev/fb). I’m confused about how to instantiate Frame Buffer II (alt_vip_cl_vfb) in the device tree, and the main problem is the reg property. This is my qsys project which compiles without errors.

Primarily, I don’t know what the size should be, but I’m not sure about the address too. I assume that it would be something like reg = <0x30000000 correct_size>;. To me, as I’m a newbie, the documentation of Frame Buffer is poor.

The second problem is that I’m confused about mapping FPGA masters connected to FPGA-to-HPS bridge. Is the address 0x30000000 correct, regarding that RAM ranges from 0x0 to 0x40000000 ?

I can’t find any example of using Frame Buffer II on Cyclone V SoC with Linux.
I’m asking for help.

I’m struggling to find the source code for the driver, else I might be able to give you some idea.
I found this
which calls out
but I can’t find that anywhere in linux-socfpga source

nor the official kernel

Did a little digging and ended up here

which led me here

Pretty esoteric piece of documentation, but maybe that can help you?
Looks to be from March, so reasonably updated?

dp_0_frame_buf: vip@0x100000280 {
	compatible = "altr,vip-frame-buffer-2.0";
	reg = <0x00000001 0x00000280 0x00000040>;
	altr,max-width = <1920>;
	altr,max-height = <1080>;
	altr,bits-per-symbol = <8>;
	altr,mem-port-width = <128>;

If that doesn’t work, this probably isn’t what you want to hear (since it sounds like you may be more firmware side than software), but you can always write your own driver. Should be able to look through the register space and allocate buffers using dma_alloc_coherent. I’m writing my own framebuffer IP right now and could give you some code for how to allocate the buffers if you need it.,0,612

With a little more digging I found the driver

And device tree binding

- reg: Physical base address and length of the framebuffer controller’s

So look in your platform designer on the H2F bus for that base address.

You good to go from here?

Thank you @jackfrye11 for suggestions and some explanation. You helped with the addresses for sure, but unfortunately it still doesn’t work. I made some changes since last time. I connected control registers to lightweight HPS-to-FPGA bridge at offset 0 - so the base address is ff200000 - and I configured framebuffer IP as Frame Reader only.
This is the current qsys project:

the address map:

and the device tree:

The problem is presented below:

[    5.541922] Unable to handle kernel NULL pointer dereference at virtual address 00000160
[    5.550015] pgd = (ptrval)
[    5.552717] [00000160] *pgd=00000000
[    5.556348] Internal error: Oops: 5 [#1] SMP ARM
[    5.560963] Modules linked in: altvipfb2_drv(+) cfbfillrect cfbimgblt cfbcopyarea
[    5.568447] CPU: 0 PID: 87 Comm: udevd Not tainted 5.12.0-altera #1
[    5.574695] Hardware name: Altera SOCFPGA
[    5.578691] PC is at dma_alloc_attrs+0x38/0x128
[    5.583223] LR is at altvipfb2_probe+0x74/0xccc [altvipfb2_drv]
[    5.589145] pc : [<c019a690>]    lr : [<bf0133a8>]    psr: 600d0013
[    5.595387] sp : c1dcbb98  ip : c1dcbbd0  fp : c1dcbbcc
[    5.600592] r10: c1a042ac  r9 : bf015014  r8 : c1a04128
[    5.605795] r7 : c1245c10  r6 : c1245c10  r5 : 00000cc0  r4 : 00000000
[    5.612295] r3 : 00000000  r2 : c1a04128  r1 : 0012c000  r0 : 00000000
[    5.618797] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
[    5.625917] Control: 10c5387d  Table: 01f4804a  DAC: 00000051
[    5.631663] Process udevd (pid: 87, stack limit = 0x(ptrval))

[    5.935027] Backtrace: 
[    5.937469] [<c019a658>] (dma_alloc_attrs) from [<bf0133a8>] (altvipfb2_probe+0x74/0xccc [altvipfb2_drv])
[    5.947030]  r8:f0821000 r7:c1245c10 r6:c1245c10 r5:00000000 r4:c1a04040
[    5.953702] [<bf013334>] (altvipfb2_probe [altvipfb2_drv]) from [<bf013198>] (altvipfb2_plat_probe+0x178/0x23c [altvipfb2_drv])
[    5.965159]  r10:00000004 r9:bf015014 r8:ef7f6d5c r7:00000000 r6:c1245c10 r5:c1245c00
[    5.972954]  r4:c1a04040
[    5.975476] [<bf013020>] (altvipfb2_plat_probe [altvipfb2_drv]) from [<c061b024>] (platform_probe+0x6c/0xc8)
[    5.985290]  r8:00000000 r7:c0dda024 r6:bf015014 r5:c1245c10 r4:00000000
[    5.991962] [<c061afb8>] (platform_probe) from [<c0618520>] (really_probe+0xf4/0x4b8)
[    5.999773]  r7:c0dda024 r6:00000000 r5:c0dda01c r4:c1245c10
[    6.005407] [<c061842c>] (really_probe) from [<c0618950>] (driver_probe_device+0x6c/0xc4)
[    6.013565]  r10:00000024 r9:c1dcbf30 r8:c1e88e48 r7:bf015014 r6:c1245c54 r5:bf015014
[    6.021360]  r4:c1245c10
[    6.023882] [<c06188e4>] (driver_probe_device) from [<c0618fc4>] (device_driver_attach+0xb8/0xc0)
[    6.032727]  r5:00000000 r4:c1245c10
[    6.036286] [<c0618f0c>] (device_driver_attach) from [<c061905c>] (__driver_attach+0x90/0x120)
[    6.044874]  r7:c0d800f0 r6:c1245c10 r5:bf015014 r4:00000000
[    6.050509] [<c0618fcc>] (__driver_attach) from [<c06161a0>] (bus_for_each_dev+0x88/0xd0)
[    6.058663]  r7:c0d800f0 r6:c0618fcc r5:bf015014 r4:00000000
[    6.064298] [<c0616118>] (bus_for_each_dev) from [<c0617dbc>] (driver_attach+0x2c/0x30)
[    6.072278]  r6:00000000 r5:c1e88480 r4:bf015014
[    6.076875] [<c0617d90>] (driver_attach) from [<c061774c>] (bus_add_driver+0x108/0x1f0)
[    6.084854] [<c0617644>] (bus_add_driver) from [<c0619ba4>] (driver_register+0x98/0x128)
[    6.092922]  r7:00000000 r6:ffffe000 r5:00000000 r4:bf015014
[    6.098556] [<c0619b0c>] (driver_register) from [<c061ad28>] (__platform_driver_register+0x2c/0x34)
[    6.107576]  r5:bf018000 r4:c0daed60
[    6.111135] [<c061acfc>] (__platform_driver_register) from [<bf018028>] (altvipfb2_driver_init+0x28/0x1000 [altvipfb2_drv])
[    6.122236] [<bf018000>] (altvipfb2_driver_init [altvipfb2_drv]) from [<c01021bc>] (do_one_initcall+0x68/0x260)
[    6.132301] [<c0102154>] (do_one_initcall) from [<c01c0b80>] (do_init_module+0x70/0x2a4)
[    6.140372]  r7:00000000 r6:00000002 r5:c11dab80 r4:bf015100
[    6.146006] [<c01c0b10>] (do_init_module) from [<c01c3368>] (load_module+0x2498/0x29a4)
[    6.153988]  r6:00000002 r5:c1e88e00 r4:00000002
[    6.158585] [<c01c0ed0>] (load_module) from [<c01c3acc>] (sys_finit_module+0xc8/0x104)
[    6.166483]  r10:0000017b r9:c1dca000 r8:c0100264 r7:0000017b r6:0000000c r5:b6e757ac
[    6.174278]  r4:00000000
[    6.176800] [<c01c3a04>] (sys_finit_module) from [<c0100060>] (ret_fast_syscall+0x0/0x58)
[    6.184951] Exception stack(0xc1dcbfa8 to 0xc1dcbff0)
[    6.189985] bfa0:                   004ce1a0 00000000 0000000c b6e757ac 00000000 004d6e38
[    6.198131] bfc0: 004ce1a0 00000000 00000000 0000017b 00020000 004d6e38 00000000 00000000
[    6.206273] bfe0: becb4d40 becb4d30 b6e6d254 b6df0220
[    6.211305]  r6:00000000 r5:00000000 r4:004ce1a0
[    6.215906] Code: e1a08002 e5933000 e50b3028 e3a03000 (e5946160) 
[    6.222018] ---[ end trace 1b5948a3b2f7d597 ]---
[    6.233084] udevd[82]: worker [87] terminated by signal 11 (Segmentation fault)
[    6.244373] udevd[82]: worker [87] failed while handling '/devices/platform/soc/'

For your Platform Designer design, is the framebuffer IP mem_master_rd interface supposed to be hooked up to the f2h_axi_slave (whose address space I think links you into a number of different things inside the chip) or is it supposed to be one of the f2h_sdram_* interfaces which go directly to the memory controller for the RAM? For my own framebuffer IP, I was connecting it to FPGA2SDRAM interfaces. What does the address map of the FPGA2HPS interface look like? Is there a way to get to the SDRAM going through that address space?

Looks like you hit some issue in your log where you were transacting from a space you shouldn’t have. If you FPGA2HPS allows you to play with chip settings and peripherals, I could easily see how you might hang the chip/trip the watchdog. Do you know how to use SignalTap? What is going on on the mem_master_rd bus right before that kernel seg fault?

I finally got it working. The problem presented previously (with memory allocation during kernel module initialization) disappeared when I switched to linux 5.4-lts version - I had been using 5.12 or 5.11 before. Then I read IP’s documentation more carefully and I realized that another blocks are needed. Now I have to generate SDK for Qt in Yocto and try to write some app.

Frame Buffer IP works fine with both interfaces ( FPGA2HPS bridge and f2h_sdram_*).
Current Platform Designer project looks like this (maybe it will help someone):