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backend/drm: don't assume possible_crtcs has only one bit set

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This isn't necessarily the case [1].

This should fix an assertion failure on Raspberry Pi 4 dual screen.

[1]: https://lists.freedesktop.org/archives/dri-devel/2020-August/275142.html

Closes: https://github.com/swaywm/wlroots/issues/1943
Co-authored-by: Simon Ser <contact@emersion.fr>
This commit is contained in:
Stephane Chauveau 2020-07-16 18:38:35 +00:00 committed by Simon Ser
parent 863acb26c0
commit b790e5ea34
1 changed files with 18 additions and 15 deletions
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33
backend/drm/drm.c
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@ -204,23 +204,26 @@ static bool init_planes(struct wlr_drm_backend *drm) {
continue;
}
/*
* This is a very naive implementation of the plane matching
* logic. Primary and cursor planes should only work on a
* single CRTC, and this should be perfectly adequate, but
* overlay planes can potentially work with multiple CRTCs,
* meaning this could return inefficient/skewed results.
*
* possible_crtcs is a bitmask of crtcs, where each bit is an
* index into drmModeRes.crtcs. So if bit 0 is set (ffs starts
* counting from 1), crtc 0 is possible.
*/
int crtc_bit = ffs(plane->possible_crtcs) - 1;
assert(drm->num_crtcs <= 32);
struct wlr_drm_crtc *crtc = NULL;
for (size_t j = 0; j < drm->num_crtcs ; j++) {
uint32_t crtc_bit = 1 << j;
if ((plane->possible_crtcs & crtc_bit) == 0) {
continue;
}
// This would be a kernel bug
assert(crtc_bit >= 0 && (size_t)crtc_bit < drm->num_crtcs);
struct wlr_drm_crtc *candidate = &drm->crtcs[j];
if ((type == DRM_PLANE_TYPE_PRIMARY && !candidate->primary) ||
(type == DRM_PLANE_TYPE_CURSOR && !candidate->cursor)) {
crtc = candidate;
break;
}
}
if (!crtc) {
drmModeFreePlane(plane);
continue;
}
struct wlr_drm_crtc *crtc = &drm->crtcs[crtc_bit];
if (!add_plane(drm, crtc, plane, type, &props)) {
drmModeFreePlane(plane);
goto error;