drm/i915/gt: Add dedicated MCR lock

We've been overloading uncore->lock to protect access to the MCR
steering register.  That's not really what uncore->lock is intended for,
and it would be better if we didn't need to hold such a high-traffic
spinlock for the whole sequence of (apply steering, access MCR register,
restore steering).  Let's create a dedicated MCR lock to protect the
steering control register over this critical section and stop relying on
the high-traffic uncore->lock.

For now the new lock is a software lock.  However some platforms (MTL
and beyond) have a hardware-provided locking mechanism that can be used
to serialize not only software accesses, but also hardware/firmware
accesses as well; support for that hardware level lock will be added in
a future patch.

v2:
 - Use irqsave/irqrestore spinlock calls; platforms using execlist
   submission rather than GuC submission can perform MCR accesses in
   interrupt context because reset -> errordump happens in a tasklet.

Cc: Chris Wilson <chris.p.wilson@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221128233014.4000136-4-matthew.d.roper@intel.com

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c b/drivers/gpu/drm/i915/gt/intel_gt.c
index 9c45afdc6e3d..42b9e2bc7477 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt.c
@@ -1087,6 +1087,7 @@ static void mmio_invalidate_full(struct intel_gt *gt)
 	enum intel_engine_id id;
 	const i915_reg_t *regs;
 	unsigned int num = 0;
+	unsigned long flags;
 
 	if (GRAPHICS_VER_FULL(i915) >= IP_VER(12, 50)) {
 		regs = NULL;
@@ -1107,7 +1108,8 @@ static void mmio_invalidate_full(struct intel_gt *gt)
 
 	intel_uncore_forcewake_get(uncore, FORCEWAKE_ALL);
 
-	spin_lock_irq(&uncore->lock); /* serialise invalidate with GT reset */
+	intel_gt_mcr_lock(gt, &flags);
+	spin_lock(&uncore->lock); /* serialise invalidate with GT reset */
 
 	awake = 0;
 	for_each_engine(engine, gt, id) {
@@ -1141,7 +1143,8 @@ static void mmio_invalidate_full(struct intel_gt *gt)
 	     IS_ALDERLAKE_P(i915)))
 		intel_uncore_write_fw(uncore, GEN12_OA_TLB_INV_CR, 1);
 
-	spin_unlock_irq(&uncore->lock);
+	spin_unlock(&uncore->lock);
+	intel_gt_mcr_unlock(gt, flags);
 
 	for_each_engine_masked(engine, gt, awake, tmp) {
 		struct reg_and_bit rb;