When the downstream VPL chain reports no modes (e.g. the panel-lvds node was runtime-disabled by board code on a unit shipped without a panel), the driver previously fell back to a 640x480 default, allocated a framebuffer, registered /dev/fb0, exported a (bogus) simplefb DT fixup to the kernel, and tried to fb_enable() the controller. fb_enable() then bailed because info->mode was NULL, but only after we'd already exported a non-functional simplefb to Linux's DRM_SIMPLEDRM and wasted ~1.2 MB on a buffer nothing scans out.
Return early from lcdif_register_fb when num_modes == 0. Drop the 640x480 fallback -- if VPL has no panel, there is nothing to scan out and a default fb is just misleading state. Signed-off-by: Johannes Schneider <[email protected]> --- A usage example where this becomes relevant and fixes a bug: we have a "modular" hardware design, where the same base-board can have either none, one or two displays bolted on - all running the same bootloader+OS. The barebox boardcode for said base-board reads a configuration eeprom and would then runtime disable the panels devicetree node - leaving the framebuffer driver without anything that has valid modes, leading to a NULL dereference. --- drivers/video/lcdif_kms.c | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-) diff --git a/drivers/video/lcdif_kms.c b/drivers/video/lcdif_kms.c index e3d1985dc9..bbdbf4eed3 100644 --- a/drivers/video/lcdif_kms.c +++ b/drivers/video/lcdif_kms.c @@ -431,18 +431,18 @@ static int lcdif_register_fb(struct lcdif_drm_private *lcdif) return ret; } - if (info->modes.num_modes) { - for (i = 0; i < info->modes.num_modes; i++) { - xmax = max(xmax, info->modes.modes[i].xres); - ymax = max(ymax, info->modes.modes[i].yres); - } - info->xres = info->modes.modes[info->modes.native_mode].xres; - info->yres = info->modes.modes[info->modes.native_mode].yres; - } else { - dev_notice(lcdif->dev, "no modes found on lcdif%d\n", lcdif->id); - xmax = info->xres = 640; - ymax = info->yres = 480; + /* no panel downstream -> nothing to scan out; stay idle */ + if (!info->modes.num_modes) { + dev_info(lcdif->dev, "no display modes from VPL, LCDIF stays idle\n"); + return 0; + } + + for (i = 0; i < info->modes.num_modes; i++) { + xmax = max(xmax, info->modes.modes[i].xres); + ymax = max(ymax, info->modes.modes[i].yres); } + info->xres = info->modes.modes[info->modes.native_mode].xres; + info->yres = info->modes.modes[info->modes.native_mode].yres; lcdif->line_length = xmax * (info->bits_per_pixel >> 3); lcdif->max_yres = ymax; -- 2.43.0
