On 03/11/2023 23:03, Dmitry Baryshkov wrote:
Supporting DP/USB-C can result in a chain of several transparent
bridges (PHY, redrivers, mux, etc). All attempts to implement DP support
in a different way resulted either in series of hacks or in device tree
not reflecting the actual hardware design. This results in drivers
having similar boilerplate code for such bridges.
Next, these drivers are susceptible to -EPROBE_DEFER loops: the next
bridge can either be probed from the bridge->attach callback, when it is
too late to return -EPROBE_DEFER, or from the probe() callback, when the
next bridge might not yet be available, because it depends on the
resources provided by the probing device. Device links can not fully
solve this problem since there are mutual dependencies between adjancent
devices.
Last, but not least, this results in the the internal knowledge of DRM
subsystem slowly diffusing into other subsystems, like PHY or USB/TYPEC.
To solve all these issues, define a separate DRM helper, which creates
separate aux device just for the bridge. During probe such aux device
doesn't result in the EPROBE_DEFER loops. Instead it allows the device
drivers to probe properly, according to the actual resource
dependencies. The bridge auxdevs are then probed when the next bridge
becomes available, sparing drivers from drm_bridge_attach() returning
-EPROBE_DEFER.
Dmitry,
Looking to give you a Tested-by: here but got the below splat.
https://git.codelinaro.org/bryan.odonoghue/kernel/-/tree/next-20231123-tcpm-fix?ref_type=heads
- Boot via fastboot
- Remove USB cable
- Attach DisplayPort cable
- Get some activity on the DP
- Then this
root@linaro-gnome:~# [ 376.861822] xhci-hcd xhci-hcd.4.auto: xHCI Host
Controller
[ 376.867584] xhci-hcd xhci-hcd.4.auto: new USB bus registered,
assigned bus number 3
[ 376.875775] xhci-hcd xhci-hcd.4.auto: hcc params 0x0230ffe5 hci
version 0x110 quirks 0x0000000000000010
[ 376.885666] xhci-hcd xhci-hcd.4.auto: irq 229, io mem 0x0a600000
[ 376.892140] xhci-hcd xhci-hcd.4.auto: xHCI Host Controller
[ 376.897951] xhci-hcd xhci-hcd.4.auto: new USB bus registered,
assigned bus number 4
[ 376.905869] xhci-hcd xhci-hcd.4.auto: Host supports USB 3.1 Enhanced
SuperSpeed
[ 376.914130] hub 3-0:1.0: USB hub found
[ 376.918030] hub 3-0:1.0: 1 port detected
[ 376.922417] usb usb4: We don't know the algorithms for LPM for this
host, disabling LPM.
[ 376.931540] hub 4-0:1.0: USB hub found
[ 376.935439] hub 4-0:1.0: 1 port detected
[ 377.885638] Unable to handle kernel NULL pointer dereference at
virtual address 0000000000000060
[ 377.892927] msm_dpu ae01000.display-controller: [drm] Cannot find any
crtc or sizes
[ 377.894724] Mem abort info:
[ 377.905504] ESR = 0x0000000096000004
[ 377.909375] EC = 0x25: DABT (current EL), IL = 32 bits
[ 377.914852] SET = 0, FnV = 0
[ 377.918005] EA = 0, S1PTW = 0
[ 377.921250] FSC = 0x04: level 0 translation fault
[ 377.926269] Data abort info:
[ 377.929239] ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
[ 377.934881] CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[ 377.940095] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[ 377.945563] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000101992000
[ 377.952441] [0000000000000060] pgd=0000000000000000, p4d=0000000000000000
[ 377.959448] Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
[ 377.965882] Modules linked in: typec_displayport nf_tables libcrc32c
nfnetlink q6asm_dai q6routing q6afe_clocks q6afe_dai q6asm q6adm
snd_q6dsp_common q6afe q6core apr pdr_interfacer
[ 377.965984] aux_bridge crct10dif_ce snd_soc_lpass_macro_common
drm_kms_helper qnoc_sm8250 qcom_wdt icc_osm_l3 fuse drm backlight dm_mod
ip_tables x_tables
[ 378.072201] CPU: 5 PID: 379 Comm: dp_hpd_handler Not tainted
6.7.0-rc2-next-20231123-00008-g812004aeedc0-dirty #30
[ 378.082817] Hardware name: Qualcomm Technologies, Inc. Robotics RB5 (DT)
[ 378.088884] msm_dpu ae01000.display-controller: [drm] Cannot find any
crtc or sizes
[ 378.089697] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS
BTYPE=--)
[ 378.089700] pc : drm_object_property_set_value+0x0/0x88 [drm]
[ 378.110607] lr : drm_dp_set_subconnector_property+0x58/0x64
[drm_display_helper]
[ 378.118205] sp : ffff800081fbbda0
[ 378.121616] x29: ffff800081fbbda0 x28: 0000000000000000 x27:
0000000000000000
[ 378.128940] x26: 0000000000000000 x25: 0000000000000000 x24:
ffff38d1ccef2880
[ 378.136264] x23: ffff38d1ccef2a10 x22: ffff38d1ccef2880 x21:
ffff38d1ccef29f0
[ 378.143587] x20: 0000000000000000 x19: ffff38d1ccef2880 x18:
0000000000000000
[ 378.150911] x17: 000000040044ffff x16: ffffa79c03e1fe34 x15:
0000000000000000
[ 378.158235] x14: ffff38d1c5861000 x13: 00000000000003ec x12:
0000000000000001
[ 378.165560] x11: 071c71c71c71c71c x10: 0000000000000b00 x9 :
ffff800081fbb9d0
[ 378.172884] x8 : ffffa79b9b4d9000 x7 : 0000000000000001 x6 :
ffffa79b9b6d74b0
[ 378.180207] x5 : 0000000000000000 x4 : ffff38d1cb2d3800 x3 :
ffff38d1c28e169f
[ 378.187530] x2 : 000000000000000f x1 : 0000000000000000 x0 :
ffff38d1cb2d3840
[ 378.194853] Call trace:
[ 378.197376] drm_object_property_set_value+0x0/0x88 [drm]
[ 378.202947] dp_display_process_hpd_high+0xa0/0x14c [msm]
[ 378.208526] dp_hpd_plug_handle.isra.0+0x8c/0x10c [msm]
[ 378.213918] hpd_event_thread+0xc4/0x56c [msm]
[ 378.218508] kthread+0x110/0x114
[ 378.221828] ret_from_fork+0x10/0x20
[ 378.225506] Code: 128002a0 d65f03c0 d4210000 17ffffea (f9403024)
[ 378.231763] ---[ end trace 0000000000000000 ]---
[ 384.505974] msm_dpu ae01000.display-controller: [drm] Cannot find any
crtc or sizes
[ 385.538016] msm_dpu ae01000.display-controller: [drm] Cannot find any
crtc or sizes
[ 385.666018] msm_dpu ae01000.display-controller: [drm] Cannot find any
crtc or sizes
