Re: drm/vc4: false-positive negative cursor position warning

[Eric Anholt]

Daniel J Blueman  writes:

> Hi Eric et al,
>
> In a number of windowing environments (eg GNOME 3) on Raspberry Pi 3B
> on 4.16.0 arm64, the mouse cursor top-left gets down to x,y -4,-4,
> tripping WARN_ON_ONCE(plane->state->crtc_x < 0 || plane->state->crtc_y
> < 0) [1], which therefore seems false-positive.
>
> Git history doesn't turn up any reason, eg it could cause undefined
> hardware behaviour, which it doesn't appear to, so would it be better
> to drop the warning, or adjust it to trip on x or y < -4 or so? If so,
> I'll prepare a patch to adjust it.

Ccing Boris, who's been doing work on the async update path.

Take a look at vc4_plane_setup_clipping_and_scaling(state) -- that has
the corrections necessary for negative x/y.  We're calling that too late
(through the avc4_plane_atomic_check() path) for this function's usage
of the offsets[].

Since it affects the computed src_w/h, we'd have to update those as well
in our async update.  Our async update is racy in a way that makes me
uncomfortable -- the HVS could process our display list at any point in
our writel() sequence, which is not very atomic.  Maybe we should be
using a double-buffered HVS display list per element, and then have the
main display list jump into each element's current display list and back
out, so that we can do async flips to new plane state by just commiting
a single writel() to the new HVS display element list.


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drm/vc4: false-positive negative cursor position warning

[Daniel J Blueman]

Hi Eric et al,

In a number of windowing environments (eg GNOME 3) on Raspberry Pi 3B
on 4.16.0 arm64, the mouse cursor top-left gets down to x,y -4,-4,
tripping WARN_ON_ONCE(plane->state->crtc_x < 0 || plane->state->crtc_y
< 0) [1], which therefore seems false-positive.

Git history doesn't turn up any reason, eg it could cause undefined
hardware behaviour, which it doesn't appear to, so would it be better
to drop the warning, or adjust it to trip on x or y < -4 or so? If so,
I'll prepare a patch to adjust it.

[Side note: simply opening the GNOME 3 Activities menu with
libgl1-mesa-dri 17.3.7 is a reliable way to reproduce "[drm] Resetting
GPU"]

Thanks,
  Dan

-- [1]

WARNING: CPU: 3 PID: 966 at drivers/gpu/drm/vc4/vc4_plane.c:771
vc4_plane_async_set_fb+0x98/0xa0
CPU: 3 PID: 966 Comm: Xorg Tainted: G S   4.16.0+ #13
Hardware name: Raspberry Pi 3 Model B Rev 1.2 (DT)
pstate: 0005 (nzcv daif -PAN -UAO)
pc : vc4_plane_async_set_fb+0x98/0xa0
lr : vc4_plane_async_set_fb+0x4c/0xa0
sp : 086ab9b0
x29: 086ab9b0 x28: 
x27: 0009 x26: fffc
x25: a81b36ca8b00 x24: a81b30667c00
x23: 0040 x22: a81b30790400
x21: a81b36ca8b00 x20: a81b30a53018
x19: a81b30667c00 x18: 
x17: b4fcec50 x16: 3447cc0e8588
x15: 3447d14fbf88 x14: 344851bb337f
x13: 3447d1bb338d x12: 3447d153b000
x11: 3447d14fc7f0 x10: 3447ccb3dac8
x9 : ffd0 x8 : 0005
x7 : 3932373639343932 x6 : 056e
x5 :  x4 : 
x3 :  x2 : ed59bd53d8905e00
x1 : fffc x0 : a81b30667c00
Call trace:
 vc4_plane_async_set_fb+0x98/0xa0
 vc4_update_plane+0x124/0x1a0
 __setplane_internal+0x1f4/0x260
 drm_mode_cursor_universal+0xf4/0x220
 drm_mode_cursor_common+0x19c/0x218
 drm_mode_cursor2_ioctl+0x34/0x48
 drm_ioctl_kernel+0x70/0xd8
 drm_ioctl+0x30c/0x438
 do_vfs_ioctl+0xc4/0x880
 SyS_ioctl+0x8c/0xa8
 el0_svc_naked+0x30/0x34
-- 
Daniel J Blueman
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