On Fri, 24 Nov 2023 at 14:23, Bryan O'Donoghue <bryan.odonoghue@xxxxxxxxxx> 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@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
