[PATCH v2 10/16] drm/exynos: implement a drm bridge

Mon Sep 14 12:31:19 UTC 2020

Hi,

On 14.09.2020 10:29, Marek Szyprowski wrote:
> On 11.09.2020 15:54, Michael Tretter wrote:
>> Make the exynos_dsi driver a full drm bridge that can be found and used
>> from other drivers.
>>
>> Other drivers can only attach to the bridge, if a mipi dsi device
>> already attached to the bridge. This allows to defer the probe of the
>> display pipe until the downstream bridges are available, too.
>>
>> Signed-off-by: Michael Tretter <m.tretter at pengutronix.de>
> This one (and the whole series applied) still fails on Exynos boards:
>
> [drm] Exynos DRM: using 11c00000.fimd device for DMA mapping operations
> exynos-drm exynos-drm: bound 11c00000.fimd (ops fimd_component_ops)
> OF: graph: no port node found in /soc/dsi at 11c80000
> 8<--- cut here ---
> Unable to handle kernel NULL pointer dereference at virtual address 00000084
> pgd = (ptrval)
> [00000084] *pgd=00000000
> Internal error: Oops: 5 [#1] PREEMPT SMP ARM
> Modules linked in:
> CPU: 1 PID: 1 Comm: swapper/0 Not tainted
> 5.9.0-rc4-next-20200911-00010-g417dc70d70ec #1608
> Hardware name: Samsung Exynos (Flattened Device Tree)
> PC is at drm_bridge_attach+0x18/0x164
> LR is at exynos_dsi_bind+0x88/0xa8
> pc : [<c0628c08>]    lr : [<c064d560>]    psr: 20000013
> sp : ef0dfca8  ip : 00000002  fp : c13190e0
> r10: 00000000  r9 : ee46d580  r8 : c13190e0
> r7 : ee438800  r6 : 00000018  r5 : ef253810  r4 : ef39e840
> r3 : 00000000  r2 : 00000018  r1 : ef39e888  r0 : ef39e840
> Flags: nzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
> Control: 10c5387d  Table: 4000404a  DAC: 00000051
> Process swapper/0 (pid: 1, stack limit = 0x(ptrval))
> Stack: (0xef0dfca8 to 0xef0e0000)
> ...
> [<c0628c08>] (drm_bridge_attach) from [<c064d560>]
> (exynos_dsi_bind+0x88/0xa8)
> [<c064d560>] (exynos_dsi_bind) from [<c066a800>]
> (component_bind_all+0xfc/0x290)
> [<c066a800>] (component_bind_all) from [<c0649dc0>]
> (exynos_drm_bind+0xe4/0x19c)
> [<c0649dc0>] (exynos_drm_bind) from [<c066ad74>]
> (try_to_bring_up_master+0x1e4/0x2c4)
> [<c066ad74>] (try_to_bring_up_master) from [<c066b2b4>]
> (component_master_add_with_match+0xd4/0x108)
> [<c066b2b4>] (component_master_add_with_match) from [<c0649ae8>]
> (exynos_drm_platform_probe+0xe4/0x110)
> [<c0649ae8>] (exynos_drm_platform_probe) from [<c0674e6c>]
> (platform_drv_probe+0x6c/0xa4)
> [<c0674e6c>] (platform_drv_probe) from [<c067242c>]
> (really_probe+0x200/0x4fc)
> [<c067242c>] (really_probe) from [<c06728f0>]
> (driver_probe_device+0x78/0x1fc)
> [<c06728f0>] (driver_probe_device) from [<c0672cd8>]
> (device_driver_attach+0x58/0x60)
> [<c0672cd8>] (device_driver_attach) from [<c0672dbc>]
> (__driver_attach+0xdc/0x174)
> [<c0672dbc>] (__driver_attach) from [<c06701b4>]
> (bus_for_each_dev+0x68/0xb4)
> [<c06701b4>] (bus_for_each_dev) from [<c06714e8>]
> (bus_add_driver+0x158/0x214)
> [<c06714e8>] (bus_add_driver) from [<c0673c1c>] (driver_register+0x78/0x110)
> [<c0673c1c>] (driver_register) from [<c0649ca8>]
> (exynos_drm_init+0xe4/0x118)
> [<c0649ca8>] (exynos_drm_init) from [<c0102484>]
> (do_one_initcall+0x8c/0x42c)
> [<c0102484>] (do_one_initcall) from [<c11011c0>]
> (kernel_init_freeable+0x190/0x1dc)
> [<c11011c0>] (kernel_init_freeable) from [<c0af7880>]
> (kernel_init+0x8/0x118)
> [<c0af7880>] (kernel_init) from [<c0100114>] (ret_from_fork+0x14/0x20)
> Exception stack(0xef0dffb0 to 0xef0dfff8)
> ...
> ---[ end trace ee27f313f9ed9da1 ]---
>
> # arm-linux-gnueabi-addr2line -e vmlinux c0628c08
> drivers/gpu/drm/drm_bridge.c:184 (discriminator 1)
>
> I will try to debug it a bit more today.

The above crash has been caused by lack of in_bridge initialization to 
NULL in exynos_dsi_bind() in this patch. However, fixing it reveals 
another issue:

[drm] Exynos DRM: using 11c00000.fimd device for DMA mapping operations
exynos-drm exynos-drm: bound 11c00000.fimd (ops fimd_component_ops)
OF: graph: no port node found in /soc/dsi at 11c80000
8<--- cut here ---
Unable to handle kernel NULL pointer dereference at virtual address 00000280
pgd = (ptrval)
[00000280] *pgd=00000000
Internal error: Oops: 5 [#1] PREEMPT SMP ARM
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 
5.9.0-rc4-next-20200911-00010-g417dc70d70ec-dirty #1613
Hardware name: Samsung Exynos (Flattened Device Tree)
PC is at __mutex_lock+0x54/0xb18
LR is at lock_is_held_type+0x80/0x138
pc : [<c0afc920>]    lr : [<c0af63e8>]    psr: 60000013
sp : ef0dfd30  ip : 33937b74  fp : c13193c8
r10: c1208eec  r9 : 00000000  r8 : ee45f808
r7 : c19561a4  r6 : 00000000  r5 : 00000000  r4 : 0000024c
r3 : 00000000  r2 : 00204140  r1 : c124f13c  r0 : 00000000
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 10c5387d  Table: 4000404a  DAC: 00000051
Process swapper/0 (pid: 1, stack limit = 0x(ptrval))
Stack: (0xef0dfd30 to 0xef0e0000)
...
[<c0afc920>] (__mutex_lock) from [<c0afd400>] (mutex_lock_nested+0x1c/0x24)
[<c0afd400>] (mutex_lock_nested) from [<c064d4b8>] 
(__exynos_dsi_host_attach+0x20/0x6c)
[<c064d4b8>] (__exynos_dsi_host_attach) from [<c064d914>] 
(exynos_dsi_host_attach+0x70/0x194)
[<c064d914>] (exynos_dsi_host_attach) from [<c0656b64>] 
(s6e8aa0_probe+0x1b0/0x218)
[<c0656b64>] (s6e8aa0_probe) from [<c0672530>] (really_probe+0x200/0x4fc)
[<c0672530>] (really_probe) from [<c06729f4>] 
(driver_probe_device+0x78/0x1fc)
[<c06729f4>] (driver_probe_device) from [<c0672ddc>] 
(device_driver_attach+0x58/0x60)
[<c0672ddc>] (device_driver_attach) from [<c0672ec0>] 
(__driver_attach+0xdc/0x174)
[<c0672ec0>] (__driver_attach) from [<c06702b8>] 
(bus_for_each_dev+0x68/0xb4)
[<c06702b8>] (bus_for_each_dev) from [<c06715ec>] 
(bus_add_driver+0x158/0x214)
[<c06715ec>] (bus_add_driver) from [<c0673d20>] (driver_register+0x78/0x110)
[<c0673d20>] (driver_register) from [<c0102484>] 
(do_one_initcall+0x8c/0x42c)
[<c0102484>] (do_one_initcall) from [<c11011c0>] 
(kernel_init_freeable+0x190/0x1dc)
[<c11011c0>] (kernel_init_freeable) from [<c0af7988>] 
(kernel_init+0x8/0x118)
[<c0af7988>] (kernel_init) from [<c0100114>] (ret_from_fork+0x14/0x20)
Exception stack(0xef0dffb0 to 0xef0dfff8)
...
---[ end trace c06e996ec2e8234d ]---

This means that dsi->encoder.dev is not initialized in 
__exynos_dsi_host_attach().

This happens, because drm_bridge_attach() in exynos_dsi_bind() returned 
earlier -517 (deferred probe), what causes cleanup of encoder and 
release of all drm resources.

Then however, the panel tries to register itself and 
exynos_dsi_host_attach() tries to access the released encoder (which is 
zeroed in drm_encoder_release) and rest of resources, what causes failure.

It looks that something is missing. Maybe mipi host has to be registered 
later, when bridge is ready? I have no idea how it is handled before 
this patch. Andrzej, could you comment it a bit?

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland