drm/i915/dp_mst: Work around Thunderbolt sink disconnect after SINK_COUNT_ESI read

[ Upstream commit 9cb15478916e849d62a6ec44b10c593b9663328c ]

Due to a problem in the iTBT DP-in adapter's firmware the sink on a TBT
link may get disconnected inadvertently if the SINK_COUNT_ESI and the
DP_LINK_SERVICE_IRQ_VECTOR_ESI0 registers are read in a single AUX
transaction. Work around the issue by reading these registers in
separate transactions.

The issue affects MTL+ platforms and will be fixed in the DP-in adapter
firmware, however releasing that firmware fix may take some time and is
not guaranteed to be available for all systems. Based on this apply the
workaround on affected platforms.

See HSD #13013007775.

v2: Cc'ing Mika Westerberg.

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13760
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14147
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://lore.kernel.org/r/20250519133417.1469181-1-imre.deak@intel.com
(cherry picked from commit c3a48363cf1f76147088b1adb518136ac5df86a0)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 3390814de0a544f3839240481f43c279143559de..cc1bbf70477b021aca4b28e98bda87a7962805ac 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2215,9 +2215,6 @@ EXPORT_PER_CPU_SYMBOL(__stack_chk_guard);
 
 #endif /* CONFIG_X86_64 */
 
-/*
- * Clear all 6 debug registers:
- */
 static void initialize_debug_regs(void)
 {
        /* Control register first -- to make sure everything is disabled. */