On Mon, 11 Apr 2022, Emmanuel Dreyfus wrote:
When the kernel initialize a framebuffer, the signal ouput changes a bit
fro mwhat is inherited from the BIOS. I face the situation where the
display looses the signal, and I suspect this is related to the refresh
rate.
OK, I'm able to get a usable UEFI console (intelfb) with the hack below
(starting X, however, immediately locks up the system):
```
diff -urN a/sys/external/bsd/drm2/dist/drm/i915/display/intel_lvds.c
b/sys/external/bsd/drm2/dist/drm/i915/display/intel_lvds.c
--- a/sys/external/bsd/drm2/dist/drm/i915/display/intel_lvds.c 2021-12-18
23:45:30.000000000 +0000
+++ b/sys/external/bsd/drm2/dist/drm/i915/display/intel_lvds.c 2022-04-12
10:28:48.162488466 +0000
@@ -962,11 +962,6 @@
if (fixed_mode)
goto out;
- /* Failed to get EDID, what about VBT? */
- fixed_mode = intel_panel_vbt_fixed_mode(intel_connector);
- if (fixed_mode)
- goto out;
-
/*
* If we didn't get EDID, try checking if the panel is already turned
* on. If so, assume that whatever is currently programmed is the
@@ -977,8 +972,12 @@
DRM_DEBUG_KMS("using current (BIOS) mode: ");
drm_mode_debug_printmodeline(fixed_mode);
fixed_mode->type |= DRM_MODE_TYPE_PREFERRED;
+ goto out;
}
+ /* Failed to get current mode, what about VBT? */
+ fixed_mode = intel_panel_vbt_fixed_mode(intel_connector);
+
/* If we still don't have a mode after all that, give up. */
if (!fixed_mode)
goto failed;
```
Going by the kernel messages, on 9.2, the old DRM fails to find a VBT:
```
kern info: [drm] failed to find VBIOS tables
i915drmkms0: interrupting at ioapic0 pin 16 (i915drmkms0)
intelfb0 at i915drmkms0
intelfb0: framebuffer at 0xffffd700687fb000, size 1366x768, depth 32,
stride 5504
kern error:
[drm:(/usr/src/sys/external/bsd/drm2/dist/drm/i915/intel_fifo_underrun.c:230)cpt_set_fifo_underrun_reporting]
*ERROR* uncleared pch fifo underrun on pch transcoder A
kern error:
[drm:(/usr/src/sys/external/bsd/drm2/dist/drm/i915/intel_fifo_underrun.c:381)intel_pch_fifo_underrun_irq_handler]
*ERROR* PCH transcoder A FIFO underrun
wsdisplay0 at intelfb0 kbdmux 1: console (default, vt100 emulation), using
wskbd0
```
but, somehow still picks the correct native mode (1366x768) and everything
is fine. The new DRM code, _does_ seem to find a VBT, but picks a
non-native resolution (1024x768) in UEFI mode and the display gets messed
up. In CSM mode, 1366x768 is correctly picked from the VBT.
I'll try to chase this down further when I have the time, but, somebody who
_knows_ this stuff would obviously make quicker progress.
-RVP
