linux-kernel - Re: [PATCH v2 2/2] drm/i915/display: Disable display for iMac's

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Message-ID: <aXozN_-GCw4bLjmE@wunner.de>
Date: Wed, 28 Jan 2026 17:03:03 +0100
From: Lukas Wunner <lukas@...ner.de>
To: Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc: Jani Nikula <jani.nikula@...ux.intel.com>,
	Atharva Tiwari <atharvatiwarilinuxdev@...il.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	Tvrtko Ursulin <tursulin@...ulin.net>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Javier Martinez Canillas <javierm@...hat.com>,
	"Borislav Petkov (AMD)" <bp@...en8.de>,
	Lenny Szubowicz <lszubowi@...hat.com>,
	Francesco Pompo <francescopompo2@...il.com>,
	linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
	intel-gfx@...ts.freedesktop.org, intel-xe@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 2/2] drm/i915/display: Disable display for iMac's

On Wed, Jan 28, 2026 at 05:37:18PM +0200, Ville Syrjälä wrote:
> On Wed, Jan 28, 2026 at 05:23:51PM +0200, Jani Nikula wrote:
> > On Wed, 28 Jan 2026, Atharva Tiwari <atharvatiwarilinuxdev@...il.com> wrote:
> > > Disable display on iMacs, as they can't do link training
> > > on the internal display.
> > >
> > > (tested on iMac20,1)
> 
> I guess the main problem with a hack like this is that you won't
> be able to get deep pkgC states due to the display hardware not
> going into DC5/6.

If patch [1/2] in this series results in a power regression,
I'd say it needs to be reworked.  Either exclude iMacs from
the set_os protocol or find a way to power down the iGPU again
once the kernel has assumed control.

I wonder what macOS does.  If the iGPU is exposed by set_os,
surely macOS must be able to power down the iGPU again,
so we should be doing the same.

Thanks,

Lukas