[PATCH v6 0/6] drm: simplify support for transparent DRM bridges

Fri Nov 24 12:33:34 UTC 2023

On Fri, 24 Nov 2023 at 14:23, Bryan O'Donoghue
<bryan.odonoghue at linaro.org> wrote:
>
> 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.

This should be fixed by
https://gitlab.freedesktop.org/drm/msm/-/tags/drm-msm-fixes-2023-11-21

>
> 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 at 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
>
>


-- 
With best wishes
Dmitry