[Intel-gfx] [RFC] drm/i915: Fix assert_plane() warning on bootup with external display

[Jani Nikula]

On Sun, 17 Jun 2018, Azhar Shaikh <azhar.shaikh at intel.com> wrote:
> On KBL, WHL RVPs, booting up with an external display connected, triggers
> below warning. This warning is not seen during hotplug.
>
> [    3.615226] ------------[ cut here ]------------
> [    3.619829] plane 1A assertion failure (expected on, current off)
> [    3.632039] WARNING: CPU: 2 PID: 354 at drivers/gpu/drm/i915/intel_display.c:1294 assert_plane+0x71/0xbb
> [    3.633920] iwlwifi 0000:00:14.3: loaded firmware version 38.c0e03d94.0 op_mode iwlmvm
> [    3.647157] Modules linked in: iwlwifi cfg80211 btusb btrtl btbcm btintel bluetooth ecdh_generic
> [    3.647163] CPU: 2 PID: 354 Comm: frecon Not tainted 4.17.0-rc7-50176-g655af12d39c2 #3
> [    3.647165] Hardware name: Intel Corporation CoffeeLake Client Platform/WhiskeyLake U DDR4 ERB, BIOS CNLSFWR1.R00.X140.B00.1804040304 04/04/2018
> [    3.684509] RIP: 0010:assert_plane+0x71/0xbb
> [    3.764451] Call Trace:
> [    3.766888]  intel_atomic_commit_tail+0xa97/0xb77
> [    3.771569]  intel_atomic_commit+0x26a/0x279
> [    3.771572]  drm_atomic_helper_set_config+0x5c/0x76
> [    3.780670]  __drm_mode_set_config_internal+0x66/0x109
> [    3.780672]  drm_mode_setcrtc+0x4c9/0x5cc
> [    3.780674]  ? drm_mode_getcrtc+0x162/0x162
> [    3.789774]  ? drm_mode_getcrtc+0x162/0x162
> [    3.798108]  drm_ioctl_kernel+0x8d/0xe4
> [    3.801926]  drm_ioctl+0x27d/0x368
> [    3.805311]  ? drm_mode_getcrtc+0x162/0x162
> [    3.805314]  ? selinux_file_ioctl+0x14e/0x199
> [    3.805317]  vfs_ioctl+0x21/0x2f
> [    3.813812]  do_vfs_ioctl+0x491/0x4b4
> [    3.813813]  ? security_file_ioctl+0x37/0x4b
> [    3.813816]  ksys_ioctl+0x55/0x75
> [    3.820672]  __x64_sys_ioctl+0x1a/0x1e
> [    3.820674]  do_syscall_64+0x51/0x5f
> [    3.820678]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [    3.828221] RIP: 0033:0x7b5e04953967
> [    3.835504] RSP: 002b:00007fff2eafb6f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> [    3.835505] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007b5e04953967
> [    3.835505] RDX: 00007fff2eafb730 RSI: 00000000c06864a2 RDI: 000000000000000f
> [    3.835506] RBP: 00007fff2eafb720 R08: 0000000000000000 R09: 0000000000000000
> [    3.835507] R10: 0000000000000070 R11: 0000000000000246 R12: 000000000000000f
> [    3.879988] R13: 000056bc9dd7d210 R14: 00007fff2eafb730 R15: 00000000c06864a2
> [    3.887081] Code: 48 c7 c7 06 71 a5 be 84 c0 48 c7 c2 06 fd a3 be 48 89 f9 48 0f 44 ca 84 db 48 0f 45 d7 48 c7 c7 df d3 a4 be 31 c0 e8 af a0 c0 ff <0f> 0b eb 2b 48 c7 c7 06 fd a3 be 84 c0 48 c7 c2 06 71 a5 be 48
> [    3.905845] WARNING: CPU: 2 PID: 354 at drivers/gpu/drm/i915/intel_display.c:1294 assert_plane+0x71/0xbb
> [    3.920964] ---[ end trace dac692f4ac46391a ]---
>
> The warning is seen when mode_setcrtc() is called for pipeB
> during bootup and before we get a mode_setcrtc() for pipeA,
> while doing update_crtcs() in intel_atomic_commit_tail().
> Now since, plane1A is still active after commit, update_crtcs()
> is done for pipeA and eventually update_plane() for plane1A.
>
> intel_plane_state->ctl for plane1A is not updated since set_modecrtc() is
> called for pipeB. So intel_plane_state->ctl for plane 1A will be 0x0.
> So doing an update_plane() for plane1A, will result in clearing
> PLANE_CTL_ENABLE bit, and hence the warning.
>
> To fix this warning, prior to updating the PLANE_CTL register with
> intel_plane_state->ctl value, read PLANE_CTL register, OR it with
> intel_plane_state->ctl and then write it to PLANE_CTL register
> instead of just relying on intel_plane_state->ctl value.
>
> Signed-off-by: Azhar Shaikh <azhar.shaikh at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_sprite.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
> index 344c0e709b19..b491b1fbdea1 100644
> --- a/drivers/gpu/drm/i915/intel_sprite.c
> +++ b/drivers/gpu/drm/i915/intel_sprite.c
> @@ -254,6 +254,7 @@ void intel_pipe_update_end(struct intel_crtc_state *new_crtc_state)
>  	uint32_t src_w = drm_rect_width(&plane_state->base.src) >> 16;
>  	uint32_t src_h = drm_rect_height(&plane_state->base.src) >> 16;
>  	unsigned long irqflags;
> +	u32 val;
>  
>  	/* Sizes are 0 based */
>  	src_w--;
> @@ -322,6 +323,8 @@ void intel_pipe_update_end(struct intel_crtc_state *new_crtc_state)
>  		I915_WRITE_FW(PLANE_POS(pipe, plane_id), (crtc_y << 16) | crtc_x);
>  	}
>  
> +	val = I915_READ_FW(PLANE_CTL(pipe, plane_id));
> +	plane_ctl |= val;

You get the warning backtrace from our state checker, the purpose of
which is to ensure that our software state and hardware state
match. This change defeats the purpose of the state checker by relying
on the hardware state using a read-modify-write. The states will be out
of sync and we won't even know.

The real fix, I think at least before I grab another cup of desperately
needed coffee, is to fix the state readout during probe.

BR,
Jani.

>  	I915_WRITE_FW(PLANE_CTL(pipe, plane_id), plane_ctl);
>  	I915_WRITE_FW(PLANE_SURF(pipe, plane_id),
>  		      intel_plane_ggtt_offset(plane_state) + surf_addr);

-- 
Jani Nikula, Intel Open Source Graphics Center