From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 169B6C32771 for ; Fri, 19 Aug 2022 17:01:43 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 2D5E510E4B1; Fri, 19 Aug 2022 17:01:41 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id 7CFCB10E0B1 for ; Fri, 19 Aug 2022 17:01:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1660928492; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Hsc4yRhAhZ4DbPHQFkOZPha0cv9GZ3AkjwFlq+dmc4w=; b=SS2SCBEKKqLW0c60/0k9Lyk1w6uL/YpJOsP/Rt67iN+pnopKKN1aPdYzDyVKjSGa9SaNSL kQZLUlFHDNtclCD/Yd/5g29u/0sd/KH4f4P43bVsoTEmLaJnYz/6GDL1u8EZkZCo/LUKCv 3aKI4Zlo9Cnu3WrndGGz4O9w9rZGV18= Received: from mail-qt1-f198.google.com (mail-qt1-f198.google.com [209.85.160.198]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-157-M4ZUNzQGNg2_pQA5w0MGqA-1; Fri, 19 Aug 2022 13:01:31 -0400 X-MC-Unique: M4ZUNzQGNg2_pQA5w0MGqA-1 Received: by mail-qt1-f198.google.com with SMTP id hf13-20020a05622a608d00b003214b6b3777so3835300qtb.13 for ; Fri, 19 Aug 2022 10:01:31 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc; bh=Hsc4yRhAhZ4DbPHQFkOZPha0cv9GZ3AkjwFlq+dmc4w=; b=xHx81zxub69VA32wVDevu9LHHYJfofgyFlpAOdDsZ10izddi1iuYUvCRLXf5HoFsrU 08QuUN5W/Z7RS2eZND+yunYqIRaW5HfehkJVEWmKUb+g7rbf2kY5NupFK6PEl7byw1kS qFS58FWCJV9K2PQbboPCsLidpBMyT8JcQuLB2OZf7Hz0woPrJzvRS0fGaZLGlsx/0Exw fb92ol316QEUonQ3PUIUBwCMRVZSk8S9D8vk6Vv3TrfLDn2INT7lWrWqxp6BWVTJ0cKk CIHLF45VBOSW34ESIYQPjop9tM9B6WCO4I83FcHBavsioOqnnTHqR0+cMqcusLsvWwMT rSZA== X-Gm-Message-State: ACgBeo3jdEkNW1TcgRcetG6laeuw8AQWkTHM6c+9hrvZL01Sn6+kfwfA 81tRIqRloNKoJO4osWqEeQw3kqtyKQFpbH6xQpUTL4S0n6w3GzlL2ajt7tc8vzZxg6yQxjh9Mjf Ni3LJk0BXJf01efj2UVKI3NoZUPVr7/zASBWXfDLB73jA X-Received: by 2002:a05:6214:2588:b0:477:22bd:e1e6 with SMTP id fq8-20020a056214258800b0047722bde1e6mr6941499qvb.105.1660928490867; Fri, 19 Aug 2022 10:01:30 -0700 (PDT) X-Google-Smtp-Source: AA6agR5adLa5ufq8xv5MSitmP52SMGWicDFV/f3YeImHZmgqosweVM0PWafCWIvK9R7y6580EaMkBmHeuxCslplaa6M= X-Received: by 2002:a05:6214:2588:b0:477:22bd:e1e6 with SMTP id fq8-20020a056214258800b0047722bde1e6mr6941464qvb.105.1660928490528; Fri, 19 Aug 2022 10:01:30 -0700 (PDT) MIME-Version: 1.0 References: <20220816025217.618181-1-kai.heng.feng@canonical.com> <87leror4sl.fsf@intel.com> <20220818115338.GA26586@wunner.de> In-Reply-To: <20220818115338.GA26586@wunner.de> From: Karol Herbst Date: Fri, 19 Aug 2022 19:01:19 +0200 Message-ID: Subject: Re: [PATCH] drm/i915: Switch TGL-H DP-IN to dGFX when it's supported To: Lukas Wunner X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: tvrtko.ursulin@linux.intel.com, Heikki Krogerus , David Airlie , intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, Hans de Goede , Kai-Heng Feng , dri-devel@lists.freedesktop.org, rodrigo.vivi@intel.com, Zenghui Yu Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Thu, Aug 18, 2022 at 2:09 PM Lukas Wunner wrote: > > On Tue, Aug 16, 2022 at 11:06:18AM +0300, Jani Nikula wrote: > > On Tue, 16 Aug 2022, Kai-Heng Feng wrote: > > > On mobile workstations like HP ZBook Fury G8, iGFX's DP-IN can switch to > > > dGFX so external monitors are routed to dGFX, and more monitors can be > > > supported as result. > > > > > > To switch the DP-IN to dGFX, the driver needs to invoke _DSM function 20 > > > on intel_dsm_guid2. This method is described in Intel document 632107. > > > > Is this the policy decision that we want to unconditionally make, > > though? > > In general, we handle switching of outputs between GPUs in vga_switcheroo.c > upon a request from user space via sysfs (well, debugfs currently). > It's up to users to decide which policy suits their needs best. > > That said, we never grew support to allow different switching policies for > the built-in panel and external outputs. Laptops supporting this are > rare. Older MacBook Pros introduced between 2008 and 2010 are among them: > They have separate muxes for the panel and external DP port. Our policy > is documented in a code comment in drivers/platform/x86/apple-gmux.c: > > * The external DP port is only fully switchable on the first two unibody > * MacBook Pro generations, MBP5 2008/09 and MBP6 2010. This is done by an > * `NXP CBTL06141`_ which is controlled by gmux. > [...] > * Our switching policy for the external port is that on those generations > * which are able to switch it fully, the port is switched together with the > * panel when IGD / DIS commands are issued to vga_switcheroo. It is thus > * possible to drive e.g. a beamer on battery power with the integrated GPU. > * The user may manually switch to the discrete GPU if more performance is > * needed. > * > * On all newer generations, the external port can only be driven by the > * discrete GPU. If a display is plugged in while the panel is switched to > * the integrated GPU, *both* GPUs will be in use for maximum performance. > * To decrease power consumption, the user may manually switch to the > * discrete GPU, thereby suspending the integrated GPU. > > In other words, on these older MacBook Pros, we switch the panel and > external DP port in unison, thus always allowing one of the two GPUs > to runtime suspend and save power. > > Thanks, > > Lukas > sure, but this is changing now. I do have a laptop with a muxable internal display. But this is considered to be a dynamic on demand switching thing not a boot time switch. Anyway, I am still not convinced that doing that unconditionally is what we want, especially as userspace has to support dynamic switching regardless. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9FFD4C3F6B0 for ; Fri, 19 Aug 2022 17:01:41 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9AE0810E0B1; Fri, 19 Aug 2022 17:01:40 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id 84EC210EEF9 for ; Fri, 19 Aug 2022 17:01:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1660928492; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Hsc4yRhAhZ4DbPHQFkOZPha0cv9GZ3AkjwFlq+dmc4w=; b=SS2SCBEKKqLW0c60/0k9Lyk1w6uL/YpJOsP/Rt67iN+pnopKKN1aPdYzDyVKjSGa9SaNSL kQZLUlFHDNtclCD/Yd/5g29u/0sd/KH4f4P43bVsoTEmLaJnYz/6GDL1u8EZkZCo/LUKCv 3aKI4Zlo9Cnu3WrndGGz4O9w9rZGV18= Received: from mail-qv1-f72.google.com (mail-qv1-f72.google.com [209.85.219.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-86-kEL5r21wOnKxQWi7eTrgpg-1; Fri, 19 Aug 2022 13:01:31 -0400 X-MC-Unique: kEL5r21wOnKxQWi7eTrgpg-1 Received: by mail-qv1-f72.google.com with SMTP id db3-20020a056214170300b00496c0aabfc9so2259463qvb.16 for ; Fri, 19 Aug 2022 10:01:31 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc; bh=Hsc4yRhAhZ4DbPHQFkOZPha0cv9GZ3AkjwFlq+dmc4w=; b=s+O3Z4u1wY9B0lZb6mVSR7pVQ5+RY/56meFVMum6pncFUDD6G4+pGhX2UUxoEXijCg Ie/CbPe669HOi/k0Y5/tHIJOf+zcBEoh59UtQIlXnT1hUYjYS9hxsqLhUmalEF4v0T9V TEcRe2uktXBphOrImyD7Fryy6SVHvHVRorYqYgyUDdqz4yFUCw1Pd//Oeb/RplWm8eOg aOV/wUr4DCk4EPd6HHUCiPLl2ubWr4Zt05l5i6V1PD/5jtRmV0iv92s7G9NzJyqlYGgb qhnH+QoeeA08NEkidgFFyY1Ddi9Jfy7nmMj1ncOPdWHoKolXLDNLpnIpTN9p2axixucq x85w== X-Gm-Message-State: ACgBeo0RXtPakc0imCD/3d22Dn0QgNbh3FR+5aGH6lkPjJ20PAHtvpJU 2IziNT7L3sJYu4wjtZNPEOqm2andMrMHI/g8598gBiJlr89XBo77S6ZZ24TFePHwYF6mJ5NY2sr fve8Zxtk5bTrsHFl3W153im250eDVp35O7kUr6KimpgxP X-Received: by 2002:a05:6214:2588:b0:477:22bd:e1e6 with SMTP id fq8-20020a056214258800b0047722bde1e6mr6941501qvb.105.1660928490867; Fri, 19 Aug 2022 10:01:30 -0700 (PDT) X-Google-Smtp-Source: AA6agR5adLa5ufq8xv5MSitmP52SMGWicDFV/f3YeImHZmgqosweVM0PWafCWIvK9R7y6580EaMkBmHeuxCslplaa6M= X-Received: by 2002:a05:6214:2588:b0:477:22bd:e1e6 with SMTP id fq8-20020a056214258800b0047722bde1e6mr6941464qvb.105.1660928490528; Fri, 19 Aug 2022 10:01:30 -0700 (PDT) MIME-Version: 1.0 References: <20220816025217.618181-1-kai.heng.feng@canonical.com> <87leror4sl.fsf@intel.com> <20220818115338.GA26586@wunner.de> In-Reply-To: <20220818115338.GA26586@wunner.de> From: Karol Herbst Date: Fri, 19 Aug 2022 19:01:19 +0200 Message-ID: To: Lukas Wunner X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Subject: Re: [Intel-gfx] [PATCH] drm/i915: Switch TGL-H DP-IN to dGFX when it's supported X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Heikki Krogerus , David Airlie , intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, Kai-Heng Feng , dri-devel@lists.freedesktop.org, rodrigo.vivi@intel.com, Zenghui Yu Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Thu, Aug 18, 2022 at 2:09 PM Lukas Wunner wrote: > > On Tue, Aug 16, 2022 at 11:06:18AM +0300, Jani Nikula wrote: > > On Tue, 16 Aug 2022, Kai-Heng Feng wrote: > > > On mobile workstations like HP ZBook Fury G8, iGFX's DP-IN can switch to > > > dGFX so external monitors are routed to dGFX, and more monitors can be > > > supported as result. > > > > > > To switch the DP-IN to dGFX, the driver needs to invoke _DSM function 20 > > > on intel_dsm_guid2. This method is described in Intel document 632107. > > > > Is this the policy decision that we want to unconditionally make, > > though? > > In general, we handle switching of outputs between GPUs in vga_switcheroo.c > upon a request from user space via sysfs (well, debugfs currently). > It's up to users to decide which policy suits their needs best. > > That said, we never grew support to allow different switching policies for > the built-in panel and external outputs. Laptops supporting this are > rare. Older MacBook Pros introduced between 2008 and 2010 are among them: > They have separate muxes for the panel and external DP port. Our policy > is documented in a code comment in drivers/platform/x86/apple-gmux.c: > > * The external DP port is only fully switchable on the first two unibody > * MacBook Pro generations, MBP5 2008/09 and MBP6 2010. This is done by an > * `NXP CBTL06141`_ which is controlled by gmux. > [...] > * Our switching policy for the external port is that on those generations > * which are able to switch it fully, the port is switched together with the > * panel when IGD / DIS commands are issued to vga_switcheroo. It is thus > * possible to drive e.g. a beamer on battery power with the integrated GPU. > * The user may manually switch to the discrete GPU if more performance is > * needed. > * > * On all newer generations, the external port can only be driven by the > * discrete GPU. If a display is plugged in while the panel is switched to > * the integrated GPU, *both* GPUs will be in use for maximum performance. > * To decrease power consumption, the user may manually switch to the > * discrete GPU, thereby suspending the integrated GPU. > > In other words, on these older MacBook Pros, we switch the panel and > external DP port in unison, thus always allowing one of the two GPUs > to runtime suspend and save power. > > Thanks, > > Lukas > sure, but this is changing now. I do have a laptop with a muxable internal display. But this is considered to be a dynamic on demand switching thing not a boot time switch. Anyway, I am still not convinced that doing that unconditionally is what we want, especially as userspace has to support dynamic switching regardless. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6190CC28B2B for ; Fri, 19 Aug 2022 17:42:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354698AbiHSRml (ORCPT ); Fri, 19 Aug 2022 13:42:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48308 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350894AbiHSRmT (ORCPT ); Fri, 19 Aug 2022 13:42:19 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C958C131A2A for ; Fri, 19 Aug 2022 10:01:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1660928494; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Hsc4yRhAhZ4DbPHQFkOZPha0cv9GZ3AkjwFlq+dmc4w=; b=QBoDO7sKvFahY+oIP7USeWCVRKtLoRIgVnsWontc7SOVl94zvo8MwY27OUFfERmyQljMPe lMTEds0jZglE43FylZwZxBVVmsLufK+mH/7lH7FotLy0JtOdmOZ3RUVDqzgCJh+u6B4ry7 OmxmgMYJoZfdRc1sbZc2STbjel5sDmo= Received: from mail-qt1-f199.google.com (mail-qt1-f199.google.com [209.85.160.199]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-232-vz29oyJdPXmtj3wY1RzSVw-1; Fri, 19 Aug 2022 13:01:31 -0400 X-MC-Unique: vz29oyJdPXmtj3wY1RzSVw-1 Received: by mail-qt1-f199.google.com with SMTP id fy12-20020a05622a5a0c00b00344569022f7so3822104qtb.17 for ; Fri, 19 Aug 2022 10:01:31 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc; bh=Hsc4yRhAhZ4DbPHQFkOZPha0cv9GZ3AkjwFlq+dmc4w=; b=aS6T02+qBWa9fLiDhtTwkOe6mWQrGYska9NNtFKE/YtcgPx+aHHFz/swfoxIEVYp+Z FgrLf7cCIX5sd3NUHgbW65KVM/I42Xl0HjCzBksIX4UQwNBiMDJRW5PxnKQZuF+sPfEh nmHew4JS16Z5iZ2cHFv7y2MfjPEX1Giw1Yrb4zg8PMJD1f31Bm9dFW/BpT7yXQpGRU9y hdVendvbaEo8sd1TiSPq1W5kqtbLtYw7GYf5zafMyiuJb9YgOZmF+1bLtQGk/pXaEvFO gnQd0Q0z9NLA1+Z2v75JaBTD5YE4KbPutdYhj0JlSxD1iZcbRuQjrvreoQJp0AvbraF5 ugEQ== X-Gm-Message-State: ACgBeo0Y6beQmqdknbsSajbuYTr+V4CeVc7hoKC4VYwN/IccqQDgprjM tlSJAC6o1VwEsM5u7XKQz5J5kdnqBNCBb5bIX293PORl0GjdCGn1uscI7qu761UwDUnQjnWHRcQ /Qs1yWYexwpvk+pU4pFq/ohv8YK3TkC7F6RmdPW1n X-Received: by 2002:a05:6214:2588:b0:477:22bd:e1e6 with SMTP id fq8-20020a056214258800b0047722bde1e6mr6941503qvb.105.1660928490869; Fri, 19 Aug 2022 10:01:30 -0700 (PDT) X-Google-Smtp-Source: AA6agR5adLa5ufq8xv5MSitmP52SMGWicDFV/f3YeImHZmgqosweVM0PWafCWIvK9R7y6580EaMkBmHeuxCslplaa6M= X-Received: by 2002:a05:6214:2588:b0:477:22bd:e1e6 with SMTP id fq8-20020a056214258800b0047722bde1e6mr6941464qvb.105.1660928490528; Fri, 19 Aug 2022 10:01:30 -0700 (PDT) MIME-Version: 1.0 References: <20220816025217.618181-1-kai.heng.feng@canonical.com> <87leror4sl.fsf@intel.com> <20220818115338.GA26586@wunner.de> In-Reply-To: <20220818115338.GA26586@wunner.de> From: Karol Herbst Date: Fri, 19 Aug 2022 19:01:19 +0200 Message-ID: Subject: Re: [PATCH] drm/i915: Switch TGL-H DP-IN to dGFX when it's supported To: Lukas Wunner Cc: Jani Nikula , tvrtko.ursulin@linux.intel.com, Heikki Krogerus , David Airlie , intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Hans de Goede , Kai-Heng Feng , rodrigo.vivi@intel.com, Zenghui Yu Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 18, 2022 at 2:09 PM Lukas Wunner wrote: > > On Tue, Aug 16, 2022 at 11:06:18AM +0300, Jani Nikula wrote: > > On Tue, 16 Aug 2022, Kai-Heng Feng wrote: > > > On mobile workstations like HP ZBook Fury G8, iGFX's DP-IN can switch to > > > dGFX so external monitors are routed to dGFX, and more monitors can be > > > supported as result. > > > > > > To switch the DP-IN to dGFX, the driver needs to invoke _DSM function 20 > > > on intel_dsm_guid2. This method is described in Intel document 632107. > > > > Is this the policy decision that we want to unconditionally make, > > though? > > In general, we handle switching of outputs between GPUs in vga_switcheroo.c > upon a request from user space via sysfs (well, debugfs currently). > It's up to users to decide which policy suits their needs best. > > That said, we never grew support to allow different switching policies for > the built-in panel and external outputs. Laptops supporting this are > rare. Older MacBook Pros introduced between 2008 and 2010 are among them: > They have separate muxes for the panel and external DP port. Our policy > is documented in a code comment in drivers/platform/x86/apple-gmux.c: > > * The external DP port is only fully switchable on the first two unibody > * MacBook Pro generations, MBP5 2008/09 and MBP6 2010. This is done by an > * `NXP CBTL06141`_ which is controlled by gmux. > [...] > * Our switching policy for the external port is that on those generations > * which are able to switch it fully, the port is switched together with the > * panel when IGD / DIS commands are issued to vga_switcheroo. It is thus > * possible to drive e.g. a beamer on battery power with the integrated GPU. > * The user may manually switch to the discrete GPU if more performance is > * needed. > * > * On all newer generations, the external port can only be driven by the > * discrete GPU. If a display is plugged in while the panel is switched to > * the integrated GPU, *both* GPUs will be in use for maximum performance. > * To decrease power consumption, the user may manually switch to the > * discrete GPU, thereby suspending the integrated GPU. > > In other words, on these older MacBook Pros, we switch the panel and > external DP port in unison, thus always allowing one of the two GPUs > to runtime suspend and save power. > > Thanks, > > Lukas > sure, but this is changing now. I do have a laptop with a muxable internal display. But this is considered to be a dynamic on demand switching thing not a boot time switch. Anyway, I am still not convinced that doing that unconditionally is what we want, especially as userspace has to support dynamic switching regardless.