Re: [PATCH v7 09/11] drm/mediatek: dp: Add support for embedded DisplayPort aux-bus

[Nícolas F. R. A. Prado]

On Tue, Aug 29, 2023 at 03:30:24PM +0200, Michael Walle wrote:
> Hi Nícolas,
> 
> > > But the real reason I've enabled it was because I'll get an kernel
> > > oops otherwise. I thought it might be some quirk that you'll need
> > > both,
> > > because eDP will register even if theres no display - as you've
> > > mentioned below.
> > > 
> > > Here's the splat:
> > > [    3.237064] mediatek-drm mediatek-drm.10.auto: bound
> > > 1c110000.vpp-merge
> > > (ops mtk_disp_merge_component_ops)
> > > [    3.238274] mediatek-drm mediatek-drm.8.auto: Not creating crtc 0
> > > because
> > > component 8 is disabled or missing
> > > [    3.239504] mediatek-drm mediatek-drm.8.auto: Not creating crtc 0
> > > because
> > > component 9 is disabled or missing
> > > [    3.240741] Unable to handle kernel NULL pointer dereference at
> > > virtual
> > > address 00000000000004a0
> > > [    3.241841] Mem abort info:
> > > [    3.242192]   ESR = 0x0000000096000004
> > > [    3.242662]   EC = 0x25: DABT (current EL), IL = 32 bits
> > > [    3.243328]   SET = 0, FnV = 0
> > > [    3.243710]   EA = 0, S1PTW = 0
> > > [    3.244104]   FSC = 0x04: level 0 translation fault
> > > [    3.244717] Data abort info:
> > > [    3.245078]   ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
> > > [    3.245765]   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
> > > [    3.246398]   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
> > > [    3.247063] [00000000000004a0] user address but active_mm is
> > > swapper
> > > [    3.247860] Internal error: Oops: 0000000096000004 [#1] SMP
> > > [    3.248559] Modules linked in:
> > > [    3.248945] CPU: 4 PID: 11 Comm: kworker/u16:0 Not tainted
> > > 6.5.0-rc7-next-20230821+ #2225
> > > [    3.249970] Hardware name: Kontron 3.5"-SBC-i1200 (DT)
> > > [    3.250614] Workqueue: events_unbound deferred_probe_work_func
> > > [    3.251347] pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS
> > > BTYPE=--)
> > > [    3.252220] pc : mtk_drm_crtc_dma_dev_get+0x8/0x18
> > > [    3.252824] lr : mtk_drm_bind+0x458/0x558
> > > [    3.253326] sp : ffff800082b23a20
> > > [    3.253741] x29: ffff800082b23a20 x28: ffff000002c78880 x27:
> > > ffff8000816466d0
> > > [    3.254635] x26: ffff000002c6f010 x25: 0000000000000003 x24:
> > > 0000000000000000
> > > [    3.255529] x23: ffff000002c78880 x22: 0000000000000002 x21:
> > > 0000000000000000
> > > [    3.256423] x20: ffff000006516800 x19: ffff000002c78880 x18:
> > > ffffffffffffffff
> > > [    3.257317] x17: 6f63206573756163 x16: 6562203020637472 x15:
> > > 6320676e69746165
> > > [    3.258211] x14: 726320746f4e203a x13: 676e697373696d20 x12:
> > > 726f2064656c6261
> > > [    3.259106] x11: 7369642073692039 x10: ffff80008275c0c0 x9 :
> > > ffff80008091ebf8
> > > [    3.260000] x8 : 00000000ffffefff x7 : ffff80008275c0c0 x6 :
> > > 80000000fffff000
> > > [    3.260895] x5 : 000000000000bff4 x4 : 0000000000000000 x3 :
> > > ffff000006516ae0
> > > [    3.261789] x2 : ffff000006516ae0 x1 : 0000000000000000 x0 :
> > > 0000000000000000
> > > [    3.262684] Call trace:
> > > [    3.262991]  mtk_drm_crtc_dma_dev_get+0x8/0x18
> > > [    3.263549]  try_to_bring_up_aggregate_device+0x16c/0x1e0
> > > [    3.264227]  __component_add+0xac/0x180
> > > [    3.264708]  component_add+0x1c/0x30
> > > [    3.265158]  mtk_disp_rdma_probe+0x17c/0x270
> > > [    3.265695]  platform_probe+0x70/0xd0
> > > [    3.266155]  really_probe+0x150/0x2c0
> > > [    3.266615]  __driver_probe_device+0x80/0x140
> > > [    3.267162]  driver_probe_device+0x44/0x170
> > > [    3.267687]  __device_attach_driver+0xc0/0x148
> > > [    3.268245]  bus_for_each_drv+0x88/0xf0
> > > [    3.268727]  __device_attach+0xa4/0x198
> > > [    3.269208]  device_initial_probe+0x1c/0x30
> > > [    3.269732]  bus_probe_device+0xb4/0xc0
> > > [    3.270214]  deferred_probe_work_func+0x90/0xd0
> > > [    3.270783]  process_one_work+0x144/0x3a0
> > > [    3.271289]  worker_thread+0x2ac/0x4b8
> > > [    3.271761]  kthread+0xec/0xf8
> > > [    3.272145]  ret_from_fork+0x10/0x20
> > > [    3.272597] Code: 814f7858 ffff8000 aa1e03e9 d503201f (f9425000)
> > > [    3.273361] ---[ end trace 0000000000000000 ]---
> > 
> > I tried reproducing this on mt8192-asurada-spherion and
> > mt8195-cherry-tomato but
> > wasn't able to. However, I did see another issue
> 
> Yeah sorry, I tried to reproduce my initial oops but messed my DT up
> and ended up with no path enabled at all.

No worries, thanks for sending fixes for both!

> 
[..]
> > The mtk-dpi driver populates its encoder's possible_crtcs from the
> > result of
> > mtk_drm_find_possible_crtc_by_comp(), and this function assumes the CRTC
> > for the
> > main path will always have ID 0, and the external path ID 1, but when
> > the
> > main path components are disabled, the external path CRTC becomes the
> > one with
> > ID 0.
> > 
> > So we'd need to make that function return the crtc id dynamically based
> > on
> > whether the components for each path are enabled or not.
> > 
> > With that function hacked to force the right crtc ID, I was able to have
> > a
> > working external DP, with the eDP pipeline disabled on both mt8192 and
> > mt8195.
> 
> Thanks for the hint, where to look at.
> 
> While digging through the code I realized that all the outputs and pipelines
> are harcoded. Doh. For all the mediatek SoCs. Looks like major restriction
> to
> me. E.g. there is also DSI and HDMI output on the mt8195. I looked at the
> downstream linux and there, the output is not part of the pipeline. Are you
> aware of any work in that direction?

I'm not sure I get what output and pipelines are hardcoded that you're referring
to (besides the one in the mtk-dsi/dpi driver that you already sent the patch
fixing).

And I'm not familiar with the DSI and HDMI output support on MT8195, so I can't
help with that.

Thanks,
Nícolas