linux-kernel - [RFC PATCH 3/9] apple-gmux: use first bit to check switch state

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Message-Id: <20230210044826.9834-4-orlandoch.dev@gmail.com>
Date:   Fri, 10 Feb 2023 15:48:20 +1100
From:   Orlando Chamberlain <orlandoch.dev@...il.com>
To:     platform-driver-x86@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, alsa-devel@...a-project.org
Cc:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Hawking Zhang <Hawking.Zhang@....com>,
        Andrey Grodzovsky <andrey.grodzovsky@....com>,
        Lijo Lazar <lijo.lazar@....com>,
        YiPeng Chai <YiPeng.Chai@....com>,
        Somalapuram Amaranath <Amaranath.Somalapuram@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        Bokun Zhang <Bokun.Zhang@....com>,
        Jack Xiao <Jack.Xiao@....com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Rander Wang <rander.wang@...el.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Amadeusz Sławiński 
        <amadeuszx.slawinski@...ux.intel.com>,
        Yong Zhi <yong.zhi@...el.com>, Evan Quan <evan.quan@....com>,
        Kerem Karabay <kekrby@...il.com>,
        Aditya Garg <gargaditya08@...e.com>,
        Aun-Ali Zaidi <admin@...eit.net>,
        Orlando Chamberlain <orlandoch.dev@...il.com>
Subject: [RFC PATCH 3/9] apple-gmux: use first bit to check switch state

On T2 Macs with MMIO gmux, when GMUX_PORT_SWITCH_DISPLAY is read, it can
have values of 2, 3, 4, and 5. Odd values correspond to the discrete gpu,
and even values correspond to the integrated gpu. The current logic is
that only 2 corresponds to IGD, but this doesn't work for T2 Macs.
Instead, check the first bit to determine the connected gpu.

As T2 Macs with gmux only can switch the internal display, it is
untested if this change (or a similar change) would be applicable
to GMUX_PORT_SWITCH_DDC and GMUX_PORT_SWITCH_EXTERNAL.

Signed-off-by: Orlando Chamberlain <orlandoch.dev@...il.com>
---
 drivers/platform/x86/apple-gmux.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c
index 67628104f31a..6109f4c2867c 100644
--- a/drivers/platform/x86/apple-gmux.c
+++ b/drivers/platform/x86/apple-gmux.c
@@ -332,10 +332,10 @@ static void gmux_read_switch_state(struct apple_gmux_data *gmux_data)
 	else
 		gmux_data->switch_state_ddc = VGA_SWITCHEROO_DIS;
 
-	if (gmux_read8(gmux_data, GMUX_PORT_SWITCH_DISPLAY) == 2)
-		gmux_data->switch_state_display = VGA_SWITCHEROO_IGD;
-	else
+	if (gmux_read8(gmux_data, GMUX_PORT_SWITCH_DISPLAY) & 1)
 		gmux_data->switch_state_display = VGA_SWITCHEROO_DIS;
+	else
+		gmux_data->switch_state_display = VGA_SWITCHEROO_IGD;
 
 	if (gmux_read8(gmux_data, GMUX_PORT_SWITCH_EXTERNAL) == 2)
 		gmux_data->switch_state_external = VGA_SWITCHEROO_IGD;
-- 
2.39.1