Patch "drm/i915/mcr: Hold GT forcewake during steering operations" has been added to the 6.5-stable tree

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This is a note to let you know that I've just added the patch titled

    drm/i915/mcr: Hold GT forcewake during steering operations

to the 6.5-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-i915-mcr-hold-gt-forcewake-during-steering-opera.patch
and it can be found in the queue-6.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 7bb19663c9d4e8e95f794c50d467e1fc1afbcec7
Author: Matt Roper <matthew.d.roper@xxxxxxxxx>
Date:   Thu Oct 19 10:02:42 2023 -0700

    drm/i915/mcr: Hold GT forcewake during steering operations
    
    [ Upstream commit 78cc55e0b64c820673a796635daf82c7eadfe152 ]
    
    The steering control and semaphore registers are inside an "always on"
    power domain with respect to RC6.  However there are some issues if
    higher-level platform sleep states are entering/exiting at the same time
    these registers are accessed.  Grabbing GT forcewake and holding it over
    the entire lock/steer/unlock cycle ensures that those sleep states have
    been fully exited before we access these registers.
    
    This is expected to become a formally documented/numbered workaround
    soon.
    
    Note that this patch alone isn't expected to have an immediately
    noticeable impact on MCR (mis)behavior; an upcoming pcode firmware
    update will also be necessary to provide the other half of this
    workaround.
    
    v2:
     - Move the forcewake inside the Xe_LPG-specific IP version check.  This
       should only be necessary on platforms that have a steering semaphore.
    
    Fixes: 3100240bf846 ("drm/i915/mtl: Add hardware-level lock for steering")
    Cc: Radhakrishna Sripada <radhakrishna.sripada@xxxxxxxxx>
    Cc: Jonathan Cavitt <jonathan.cavitt@xxxxxxxxx>
    Signed-off-by: Matt Roper <matthew.d.roper@xxxxxxxxx>
    Reviewed-by: Radhakrishna Sripada <radhakrishna.sripada@xxxxxxxxx>
    Reviewed-by: Jonathan Cavitt <jonathan.cavitt@xxxxxxxxx>
    Reviewed-by: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
    Link: https://patchwork.freedesktop.org/patch/msgid/20231019170241.2102037-2-matthew.d.roper@xxxxxxxxx
    (cherry picked from commit 8fa1c7cd1fe9cdfc426a603e1f1eecd3f463c487)
    Signed-off-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
index 0b414eae16831..2c0f1f3e28ff8 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
@@ -376,9 +376,26 @@ void intel_gt_mcr_lock(struct intel_gt *gt, unsigned long *flags)
 	 * driver threads, but also with hardware/firmware agents.  A dedicated
 	 * locking register is used.
 	 */
-	if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70))
+	if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70)) {
+		/*
+		 * The steering control and semaphore registers are inside an
+		 * "always on" power domain with respect to RC6.  However there
+		 * are some issues if higher-level platform sleep states are
+		 * entering/exiting at the same time these registers are
+		 * accessed.  Grabbing GT forcewake and holding it over the
+		 * entire lock/steer/unlock cycle ensures that those sleep
+		 * states have been fully exited before we access these
+		 * registers.  This wakeref will be released in the unlock
+		 * routine.
+		 *
+		 * This is expected to become a formally documented/numbered
+		 * workaround soon.
+		 */
+		intel_uncore_forcewake_get(gt->uncore, FORCEWAKE_GT);
+
 		err = wait_for(intel_uncore_read_fw(gt->uncore,
 						    MTL_STEER_SEMAPHORE) == 0x1, 100);
+	}
 
 	/*
 	 * Even on platforms with a hardware lock, we'll continue to grab
@@ -415,8 +432,11 @@ void intel_gt_mcr_unlock(struct intel_gt *gt, unsigned long flags)
 {
 	spin_unlock_irqrestore(&gt->mcr_lock, flags);
 
-	if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70))
+	if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70)) {
 		intel_uncore_write_fw(gt->uncore, MTL_STEER_SEMAPHORE, 0x1);
+
+		intel_uncore_forcewake_put(gt->uncore, FORCEWAKE_GT);
+	}
 }
 
 /**



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