WIP: Debug failure to call create_buffer_object() on Intel iGPU

[strohel]

Just some WIP debugging to see if I can get just-gl running on Intel iGPU with i915
driver.

Relates to #4.

Currently I'm getting:

prelude

[src/main.rs:89] gpu.get_driver().expect("Failed to get GPU driver info") = Driver {
    name: "i915",
    date: "20201103",
    desc: "Intel Graphics",
}
[src/main.rs:90] gpu.get_bus_id().expect("Failed to get GPU bus ID") = ""
Connectors:
        eDP-1, Connected=✅
        HDMI-A-1, Connected=❌
        DP-1, Connected=❌
        DP-2, Connected=❌
        DP-3, Connected=❌
        DP-4, Connected=❌
Using connector: eDP-1
Using mode: Mode { name: "1920x1200", clock: 156100, size: (1920, 1200), hsync: (1936, 1952, 2104), vsync: (1203, 1217, 1236), hskew: 0, vscan: 0, vrefresh: 60, mode_type: PREFERRED | DRIVER }
[src/main.rs:125] encoder = Info {
    handle: encoder::Handle(
        235,
    ),
    enc_type: TMDS,
    crtc: Some(
        crtc::Handle(
            80,
        ),
    ),
    pos_crtcs: 15,
    pos_clones: 1,
}
[src/main.rs:132] crtc = Info {
    handle: crtc::Handle(
        80,
    ),
    position: (
        0,
        0,
    ),
    mode: Some(
        Mode {
            name: "1920x1200",
            clock: 156100,
            size: (
                1920,
                1200,
            ),
            hsync: (
                1936,
                1952,
                2104,
            ),
            vsync: (
                1203,
                1217,
                1236,
            ),
            hskew: 0,
            vscan: 0,
            vrefresh: 60,
            mode_type: PREFERRED | DRIVER,
        },
    ),
    fb: Some(
        framebuffer::Handle(
            289,
        ),
    ),
    gamma_length: 256,
}

Is AB24 format supported for SCANOUT | WRITE usage: true
Is AR24 format supported for SCANOUT | WRITE usage: true
Is BG24 format supported for SCANOUT | WRITE usage: false
Is BA24 format supported for SCANOUT | WRITE usage: false
Is BX24 format supported for SCANOUT | WRITE usage: false
Is RG24 format supported for SCANOUT | WRITE usage: false
Is R8A8 format supported for SCANOUT | WRITE usage: false
Is RA24 format supported for SCANOUT | WRITE usage: false
Is RX24 format supported for SCANOUT | WRITE usage: false
Is XB24 format supported for SCANOUT | WRITE usage: true
Is XR24 format supported for SCANOUT | WRITE usage: true
gbm.create_buffer_object(width: 1920, height: 1200, format: AR24, usage: SCANOUT | WRITE)
thread 'main' panicked at src/main.rs:155:90:
called `Result::unwrap()` on an `Err` value: Os { code: 22, kind: InvalidInput, message: "Invalid argument" }

Which puzzles me, because the format and usage combination is claimed to be supported.

[mbernat]

Yeah, I don't think the formats are the issue here, we're probably not initializing something else correctly.

It would be nice to get more debug info from DRM/GBM when something goes wrong. With strace you can see a bit more but I'm afraid we'd have to read kernel code to figure out what goes wrong.

[PabloMansanet]

Just to add another data point, I'm having this exact same issue. Will investigate as well!

[PabloMansanet]

I've looked into this for a bit and I didn't really get anywhere. libgbm is a bit underdocumented, and from the examples I find it looks like we should be able to call gbm_bo_create pretty much exactly as we're doing. I might try an equivalent C example tomorrow.