Re: Commit d6e25b3590 breaks external video (HDMI) on mt8173 (chromebook oak)

Hi Andy,

On Thu, 2025-08-14 at 22:38 +0800, Chun-Kuang Hu wrote:
> Forward to dri-devel and linux-mediatek.
>=20
> Andy Chernyak <[email protected]> =E6=96=BC 2025=E5=B9=B47=E6=9C=88=
2=E6=97=A5 =E9=80=B1=E4=B8=89 =E4=B8=8B=E5=8D=8811:12=E5=AF=AB=E9=81=93=EF=
=BC=9A
> >=20
> > Kernel 6.16 has external video (both hdmi and displayport-over-
> > usbc) broken (black screen) on mt8173-based chromebooks (platform
> > codename "oak", device codename "hana"). Bisect points finger to
> > following commit:
> >=20
> > From d6e25b3590a0679bca1a1becc04e3999f1dfd461
> > From: Guillaume Ranquet <[email protected]>
> > Date: Tue, 15 Apr 2025 12:43:05 +0200
> > Subject: drm/mediatek: hdmi: Use regmap instead of iomem for main
> > registers
> > In preparation for the addition of a new version of the HDMI IP
> > which will need to share its iospace between multiple subdrivers,
> > and in preparation for moving out the common bits between the two,
> > migrate this driver to fully use regmap.
> >=20
> > Reverting d6e25b3590 with "patch -R" on top of 6.16-rc4 fixes this.

thank you for the bug report.

By reading and checking this patch changes, I found two modifications
that looked incorrect, so I sent a patch to fix them:
https://lore.kernel.org/dri-devel/20250818-mt8173-fix-hdmi-issue-v1-1-55aff=
[email protected]/

Since I don't have any mt8173-based board myself, could you test this
patch and tell if it does fix the issue (or not)?

Looking forward to your reply,

Regards,
Louis-Alexis