Re: [PATCH v10 01/11] drm/sun4i: dsi: Fix TCON DRQ set bits

[Maxime Ripard]

On Mon, May 20, 2019 at 02:33:08PM +0530, Jagan Teki wrote:
> According to "DRM kernel-internal display mode structure" in
> include/drm/drm_modes.h the current driver is trying to include
> sync timings along with front porch value while checking and
> computing drq set bits in non-burst mode.
>
> mode->hsync_end - mode->hdisplay => horizontal front porch + sync
>
> With adding additional sync timings, the dsi controller leads to
> wrong drq set bits for "bananapi,s070wv20-ct16" panel which indeed
> trigger panel flip_done timed out as:
>
>  WARNING: CPU: 0 PID: 31 at drivers/gpu/drm/drm_atomic_helper.c:1429 drm_atomic_helper_wait_for_vblanks.part.1+0x298/0x2a0
>  [CRTC:46:crtc-0] vblank wait timed out
>  Modules linked in:
>  CPU: 0 PID: 31 Comm: kworker/0:1 Not tainted 5.1.0-next-20190514-00026-g01f0c75b902d-dirty #13
>  Hardware name: Allwinner sun8i Family
>  Workqueue: events deferred_probe_work_func
>  [<c010ed54>] (unwind_backtrace) from [<c010b76c>] (show_stack+0x10/0x14)
>  [<c010b76c>] (show_stack) from [<c0688c70>] (dump_stack+0x84/0x98)
>  [<c0688c70>] (dump_stack) from [<c011d9e4>] (__warn+0xfc/0x114)
>  [<c011d9e4>] (__warn) from [<c011da40>] (warn_slowpath_fmt+0x44/0x68)
>  [<c011da40>] (warn_slowpath_fmt) from [<c040cd50>] (drm_atomic_helper_wait_for_vblanks.part.1+0x298/0x2a0)
>  [<c040cd50>] (drm_atomic_helper_wait_for_vblanks.part.1) from [<c040e694>] (drm_atomic_helper_commit_tail_rpm+0x5c/0x6c)
>  [<c040e694>] (drm_atomic_helper_commit_tail_rpm) from [<c040e4dc>] (commit_tail+0x40/0x6c)
>  [<c040e4dc>] (commit_tail) from [<c040e5cc>] (drm_atomic_helper_commit+0xbc/0x128)
>  [<c040e5cc>] (drm_atomic_helper_commit) from [<c0411b64>] (restore_fbdev_mode_atomic+0x1cc/0x1dc)
>  [<c0411b64>] (restore_fbdev_mode_atomic) from [<c04156f8>] (drm_fb_helper_restore_fbdev_mode_unlocked+0x54/0xa0)
>  [<c04156f8>] (drm_fb_helper_restore_fbdev_mode_unlocked) from [<c0415774>] (drm_fb_helper_set_par+0x30/0x54)
>  [<c0415774>] (drm_fb_helper_set_par) from [<c03ad450>] (fbcon_init+0x560/0x5ac)
>  [<c03ad450>] (fbcon_init) from [<c03eb8a0>] (visual_init+0xbc/0x104)
>  [<c03eb8a0>] (visual_init) from [<c03ed1b8>] (do_bind_con_driver+0x1b0/0x390)
>  [<c03ed1b8>] (do_bind_con_driver) from [<c03ed780>] (do_take_over_console+0x13c/0x1c4)
>  [<c03ed780>] (do_take_over_console) from [<c03ad800>] (do_fbcon_takeover+0x74/0xcc)
>  [<c03ad800>] (do_fbcon_takeover) from [<c013c9c8>] (notifier_call_chain+0x44/0x84)
>  [<c013c9c8>] (notifier_call_chain) from [<c013cd20>] (__blocking_notifier_call_chain+0x48/0x60)
>  [<c013cd20>] (__blocking_notifier_call_chain) from [<c013cd50>] (blocking_notifier_call_chain+0x18/0x20)
>  [<c013cd50>] (blocking_notifier_call_chain) from [<c03a6e44>] (register_framebuffer+0x1e0/0x2f8)
>  [<c03a6e44>] (register_framebuffer) from [<c04153c0>] (__drm_fb_helper_initial_config_and_unlock+0x2fc/0x50c)
>  [<c04153c0>] (__drm_fb_helper_initial_config_and_unlock) from [<c04158c8>] (drm_fbdev_client_hotplug+0xe8/0x1b8)
>  [<c04158c8>] (drm_fbdev_client_hotplug) from [<c0415a20>] (drm_fbdev_generic_setup+0x88/0x118)
>  [<c0415a20>] (drm_fbdev_generic_setup) from [<c043f060>] (sun4i_drv_bind+0x128/0x160)
>  [<c043f060>] (sun4i_drv_bind) from [<c044b598>] (try_to_bring_up_master+0x164/0x1a0)
>  [<c044b598>] (try_to_bring_up_master) from [<c044b668>] (__component_add+0x94/0x140)
>  [<c044b668>] (__component_add) from [<c0445e1c>] (sun6i_dsi_probe+0x144/0x234)
>  [<c0445e1c>] (sun6i_dsi_probe) from [<c0452ef4>] (platform_drv_probe+0x48/0x9c)
>  [<c0452ef4>] (platform_drv_probe) from [<c04512cc>] (really_probe+0x1dc/0x2c8)
>  [<c04512cc>] (really_probe) from [<c0451518>] (driver_probe_device+0x60/0x160)
>  [<c0451518>] (driver_probe_device) from [<c044f7a4>] (bus_for_each_drv+0x74/0xb8)
>  [<c044f7a4>] (bus_for_each_drv) from [<c045107c>] (__device_attach+0xd0/0x13c)
>  [<c045107c>] (__device_attach) from [<c0450474>] (bus_probe_device+0x84/0x8c)
>  [<c0450474>] (bus_probe_device) from [<c0450900>] (deferred_probe_work_func+0x64/0x90)
>  [<c0450900>] (deferred_probe_work_func) from [<c0135970>] (process_one_work+0x204/0x420)
>  [<c0135970>] (process_one_work) from [<c013690c>] (worker_thread+0x274/0x5a0)
>  [<c013690c>] (worker_thread) from [<c013b3d8>] (kthread+0x11c/0x14c)
>  [<c013b3d8>] (kthread) from [<c01010e8>] (ret_from_fork+0x14/0x2c)
>  Exception stack(0xde539fb0 to 0xde539ff8)
>  9fa0:                                     00000000 00000000 00000000 00000000
>  9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>  9fe0: 00000000 00000000 00000000 00000000 00000013 00000000
>  ---[ end trace b57eb1e5c64c6b8b ]---
>  random: fast init done
>  [drm:drm_atomic_helper_wait_for_dependencies] *ERROR* [CRTC:46:crtc-0] flip_done timed out
>  [drm:drm_atomic_helper_wait_for_dependencies] *ERROR* [CONNECTOR:48:DSI-1] flip_done timed out
>  [drm:drm_atomic_helper_wait_for_dependencies] *ERROR* [PLANE:30:plane-0] flip_done timed out
>
> But according to Allwinner A33, A64 BSP code [1] [3] the TCON DRQ for
> non-burst DSI mode can be computed based on "horizontal front porch"
> value only (no sync timings included).
>
> Detailed evidence for drq set bits based on A33 BSP [1] [2]
>
> => panel->lcd_ht - panel->lcd_x - panel->lcd_hbp - 20
> => (tt->hor_front_porch + lcdp->panel_info.lcd_hbp +
> lcdp->panel_info.lcd_x) - panel->lcd_x - panel->lcd_hbp - 20
> => tt->hor_front_porch - 20

The thing is, while your explanation on the DRM side is sound,
Allwinner has been using the hbp field of their panel description to
store what DRM calls the backporch and the sync period.

And nowhere in that commit log you are describing whether it's still
an issue or not, and if it's not anymore how you did test that it's
not the case anymore.

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com