Re: [PATCH] drm/mediatek: Disable AFBC support on Mediatek DRM driver

["CK Hu (胡俊光)" <ck.hu@mediatek.com>]

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Hi, Justin:

AFBC just improve DRAM bandwidth performance, so I decide to backport this disable patch.
Once fixup patch exist, then backport fixup patch.

Regards,
CK

On Tue, 2025-10-28 at 10:48 +0000, Macpaul Lin (林智斌) wrote:
> 
> On Fri, 2025-10-24 at 17:27 -0300, Ariel D'Alessandro wrote:
> > 
> > External email : Please do not click links or open attachments until
> > you have verified the sender or the content.
> > 
> > 
> > Commit c410fa9b07c32 ("drm/mediatek: Add AFBC support to Mediatek DRM
> > driver") added AFBC support to Mediatek DRM and enabled the
> > 32x8/split/sparse modifier.
> > 
> > However, this is currently broken on Mediatek MT8188 (Genio 700 EVK
> > platform); tested using upstream Kernel and Mesa (v25.2.1), AFBC is
> > used by
> > default since Mesa v25.0.
> > 
> > Kernel trace reports vblank timeouts constantly, and the render is
> > garbled:
> > 
> > ```
> > [CRTC:62:crtc-0] vblank wait timed out
> > WARNING: CPU: 7 PID: 70 at drivers/gpu/drm/drm_atomic_helper.c:1835
> > drm_atomic_helper_wait_for_vblanks.part.0+0x24c/0x27c
> > [...]
> > Hardware name: MediaTek Genio-700 EVK (DT)
> > Workqueue: events_unbound commit_work
> > pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> > pc : drm_atomic_helper_wait_for_vblanks.part.0+0x24c/0x27c
> > lr : drm_atomic_helper_wait_for_vblanks.part.0+0x24c/0x27c
> > sp : ffff80008337bca0
> > x29: ffff80008337bcd0 x28: 0000000000000061 x27: 0000000000000000
> > x26: 0000000000000001 x25: 0000000000000000 x24: ffff0000c9dcc000
> > x23: 0000000000000001 x22: 0000000000000000 x21: ffff0000c66f2f80
> > x20: ffff0000c0d7d880 x19: 0000000000000000 x18: 000000000000000a
> > x17: 000000040044ffff x16: 005000f2b5503510 x15: 0000000000000000
> > x14: 0000000000000000 x13: 74756f2064656d69 x12: 742074696177206b
> > x11: 0000000000000058 x10: 0000000000000018 x9 : ffff800082396a70
> > x8 : 0000000000057fa8 x7 : 0000000000000cce x6 : ffff8000823eea70
> > x5 : ffff0001fef5f408 x4 : ffff80017ccee000 x3 : ffff0000c12cb480
> > x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff0000c12cb480
> > Call trace:
> >  drm_atomic_helper_wait_for_vblanks.part.0+0x24c/0x27c (P)
> >  drm_atomic_helper_commit_tail_rpm+0x64/0x80
> >  commit_tail+0xa4/0x1a4
> >  commit_work+0x14/0x20
> >  process_one_work+0x150/0x290
> >  worker_thread+0x2d0/0x3ec
> >  kthread+0x12c/0x210
> >  ret_from_fork+0x10/0x20
> > ---[ end trace 0000000000000000 ]---
> > ```
> > 
> > Until this gets fixed upstream, disable AFBC support on this
> > platform, as
> > it's currently broken with upstream Mesa.
> > 
> > Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@collabora.com>
> > ---
> >  drivers/gpu/drm/mediatek/mtk_plane.c | 24 +-----------------------
> >  1 file changed, 1 insertion(+), 23 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/mediatek/mtk_plane.c
> > b/drivers/gpu/drm/mediatek/mtk_plane.c
> > index 02349bd440017..788b52c1d10c5 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_plane.c
> > +++ b/drivers/gpu/drm/mediatek/mtk_plane.c
> > @@ -21,9 +21,6 @@
> > 
> >  static const u64 modifiers[] = {
> >         DRM_FORMAT_MOD_LINEAR,
> > -       DRM_FORMAT_MOD_ARM_AFBC(AFBC_FORMAT_MOD_BLOCK_SIZE_32x8 |
> > -                               AFBC_FORMAT_MOD_SPLIT |
> > -                               AFBC_FORMAT_MOD_SPARSE),
> >         DRM_FORMAT_MOD_INVALID,
> >  };
> > 
> > @@ -71,26 +68,7 @@ static bool mtk_plane_format_mod_supported(struct
> > drm_plane *plane,
> >                                            uint32_t format,
> >                                            uint64_t modifier)
> >  {
> > -       if (modifier == DRM_FORMAT_MOD_LINEAR)
> > -               return true;
> > -
> > -       if (modifier != DRM_FORMAT_MOD_ARM_AFBC(
> > -                               AFBC_FORMAT_MOD_BLOCK_SIZE_32x8 |
> > -                               AFBC_FORMAT_MOD_SPLIT |
> > -                               AFBC_FORMAT_MOD_SPARSE))
> > -               return false;
> > -
> > -       if (format != DRM_FORMAT_XRGB8888 &&
> > -           format != DRM_FORMAT_ARGB8888 &&
> > -           format != DRM_FORMAT_BGRX8888 &&
> > -           format != DRM_FORMAT_BGRA8888 &&
> > -           format != DRM_FORMAT_ABGR8888 &&
> > -           format != DRM_FORMAT_XBGR8888 &&
> > -           format != DRM_FORMAT_RGB888 &&
> > -           format != DRM_FORMAT_BGR888)
> > -               return false;
> > -
> > -       return true;
> > +       return modifier == DRM_FORMAT_MOD_LINEAR;
> >  }
> > 
> >  static void mtk_plane_destroy_state(struct drm_plane *plane,
> > 
> 
> Great! Thanks for this patch.
> I've tested this patch against k6.17.5 on mt8395-genio-1200-evk board,
> and it is working.
> I've also tested this patch with 'modetest -M mediatek -s
> 34@59:1200x1290' is working as well.
> 
> I'm not sure if it is possible to add a "Fixes:" tag to this patch?
> Maybe add this patch with 'Cc: stable@vger.kernel.org #6.17' at least?
> Some Linux distros are currently using 6.17 for testing.
> 
> Reviewed-by: Macpaul Lin <macpaul.lin@mediatek.com>
> 
> Regards,
> Macpaul Lin
> 
> 
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