lkml.org 
[lkml]   [2022]   [Aug]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH v2 32/41] drm/vc4: vec: Convert to the new TV mode property
    Hi Maxime,

    I tested your patchset on my Pi and it mostly works. Good work! However,
    I noticed a couple of issues.

    > -static int vc4_vec_encoder_atomic_check(struct drm_encoder *encoder,
    > -                    struct drm_crtc_state *crtc_state,
    > -                    struct drm_connector_state *conn_state)
    > -{
    > -    const struct vc4_vec_tv_mode *vec_mode;
    > -
    > -    vec_mode = &vc4_vec_tv_modes[conn_state->tv.mode];
    > -
    > -    if (conn_state->crtc &&
    > -        !drm_mode_equal(vec_mode->mode, &crtc_state->adjusted_mode))
    > -        return -EINVAL;
    > -
    > -    return 0;
    > -}

    I may have said it myself that we should allow custom modelines without too
    much validation. The VC4 and VEC, however, have some considerable limitations
    when it comes to the modelines that they can reliably output.

    In particular, attempting to use "50 Hz" timings in NTSC/PAL-M modes (or
    "60 Hz" in PAL/SECAM modes) results in a weirdly skewed image. Here's how it
    may look like:
    https://user-images.githubusercontent.com/4499762/187575940-736e7262-c82d-42f3-a2d8-f309cbd51139.png

    This is because if the CRTC does not trigger the sync pulses within an
    acceptable time window, the VEC apparently generates them itself. This causes
    the VEC sync pulses (which go onto the wire) not quite line up with the ones
    from the modeline, which results in what you see on the screenshot.

    I once wrote a validation function based on extensive testing of what
    produces a sensible output and what doesn't. You can find it here:
    https://github.com/raspberrypi/linux/pull/4406/commits/15c0c51. I think it
    might be a good idea to include something like that - even though I know it's
    somewhat ugly.

    (BTW, those %2 checks on vertical timings in that linked commit can be ignored;
    those values are divided by 2 for interlaced modes anyway. Those checks were
    intended to ensure proper odd-first or even-first timings; I'm not sure if your
    code calculates those in the same way)

    >  static int vc4_vec_connector_get_modes(struct drm_connector *connector)
    >  {
    > -    struct drm_connector_state *state = connector->state;
    >      struct drm_display_mode *mode;
    > +    int count = 0;
    >  
    > -    mode = drm_mode_duplicate(connector->dev,
    > -                  vc4_vec_tv_modes[state->tv.mode].mode);
    > +    mode = drm_mode_analog_ntsc_480i(connector->dev);
    >      if (!mode) {
    >          DRM_ERROR("Failed to create a new display mode\n");
    >          return -ENOMEM;
    >      }
    >  
    >      drm_mode_probed_add(connector, mode);
    > +    count += 1;
    >  
    > -    return 1;
    > +    mode = drm_mode_analog_pal_576i(connector->dev);
    > +    if (!mode) {
    > +        DRM_ERROR("Failed to create a new display mode\n");
    > +        return -ENOMEM;
    > +    }
    > +
    > +    drm_mode_probed_add(connector, mode);
    > +    count += 1;
    > +
    > +    return count;
    > +}

    Xorg is pretty confused by these modes being reported like that. The 576i mode
    is *always* preferred, presumably because of the higher resolution. If the NTSC
    mode is set (via the kernel cmdline or just due to it being the default), this
    results in a mess on the screen - exactly the same thing as on the screenshot
    linked above.

    Note that drm_helper_probe_add_cmdline_mode() *does* add the
    DRM_MODE_TYPE_USERDEF flag to the 480i mode, having detected it as preferred
    on the command line - but Xorg does not seem to care about that.

    I remember Noralf suggesting setting DRM_MODE_TYPE_PREFERRED for the mode that
    corresponds to the currently chosen tv_mode - that would fix the problem.
    An alternative would be to _not_ add the "opposite" mode at all, like the
    current default Raspberry Pi OS kernel behaves.

    Note that if you decide to add the modeline validation like I suggested in the
    comment above, then without setting the preferred mode properly, Xorg will just
    give up and sit on a blank screen until you run xrandr from another terminal
    if tv_mode incompatible with 576i is selected.

    Best regards,
    Mateusz Kwiatkowski

    \
     
     \ /
      Last update: 2022-08-31 04:24    [W:4.108 / U:0.152 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site