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From:   Frank Wunderlich <frank-w@public-files.de>
To:     Chun-Kuang Hu <chunkuang.hu@kernel.org>
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        Dafna Hirschfeld <dafna.hirschfeld@collabora.com>,
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        Collabora Kernel ML <kernel@collabora.com>,
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Subject: Aw: Re: Re: Re: BUG: MTK DRM/HDMI broken on 5.13 (mt7623/bpi-r2)
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Date:   Mon, 12 Jul 2021 10:11:08 +0200
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Hi,

HDMI is broken again in 5.14-rc1 (of course i have applied my patch [1])

now i've got a NULL pointer dereference

[   21.883641] PC is at mtk_dpi_bridge_atomic_check+0x38/0x78
[   21.889158] LR is at drm_atomic_bridge_chain_check+0x150/0x30c

"dpi" is  not set correctly in mtk_dpi_bridge_atomic_check

this function is new since

commit ec8747c52434b69cea2b18068e72f051e23d3839
    drm/mediatek: dpi: Add bus format negotiation

i do not see where bridge->driver_private is set, but in other function it=
 is solved like this:

bridge_to_dpi(bridge)

this fixes the NULL-pointer dereference, and system starts to xserver, but=
 i do not see fbcon...it looks like drm is now initialized later (~ at log=
in prompt on serial console). i stopped lightdm and still do not see login=
prompt on hdmi, so it looks like fbcon is broken

send out fix for NULL issue, but fbcon ist still unclear...but i see this =
in dmesg:

dmesg | grep -i fbcon
[    0.000000] Kernel command line: root=3D/dev/mmcblk0p2 rw rootwait earl=
yprintk console=3DttyS0,115200 video=3D1280x1024 console=3Dtty1 fbcon=3Dma=
p:0
[    0.000000] Unknown command line parameters: fbcon=3Dmap:0
[    7.040167]     fbcon=3Dmap:0

and no framebuffer/fb0 in dmesg

regards Frank

[1] https://patchwork.kernel.org/project/linux-mediatek/patch/202107101324=
31.265985-1-linux@fw-web.de/