[PATCH 2/3] drm/panthor: Fully disable the AS even if it's going to be re-assigned

[Boris Brezillon]

We're trying to be smart by skipping the UPDATE(UNMAPPED) step, but
it remains to be proven it adds any noticeable overhead. Moreover, it's
breaking the assumption that, once the VM is unbound, no access can
happen on it.

For instance, say the panthor_mmu_as_enable() call in panthor_vm_active()
fails after we've called panthor_vm_release_as_locked(), we're now in a
state where the HW still points to the old page table, but SW slot points
to the new VM, which is not truly HW-bound.

If, after the as_slots lock is released, the evicted VM itself is
released, the HW might have access to memory that has been returned
to the system until the reset we scheduled (because of the faulty
AS_COMMAND) is effective.

Let's make this bullet-proof by doing a full bound -> unbound -> bound
cycle on AS slot recycling.

Fixes: 32e593d74c39 ("drm/panthor: Make sure caches are flushed/invalidated when an AS is recycled")
Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/panthor/panthor_mmu.c | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
index 7e98084b9a1e..038a092fd08c 100644
--- a/drivers/gpu/drm/panthor/panthor_mmu.c
+++ b/drivers/gpu/drm/panthor/panthor_mmu.c
@@ -620,8 +620,7 @@ static int panthor_mmu_as_enable(struct panthor_device *ptdev, u32 as_nr,
 	return as_send_cmd_and_wait(ptdev, as_nr, AS_COMMAND_UPDATE);
 }
 
-static int panthor_mmu_as_disable(struct panthor_device *ptdev, u32 as_nr,
-				  bool recycle_slot)
+static int panthor_mmu_as_disable(struct panthor_device *ptdev, u32 as_nr)
 {
 	struct panthor_mmu *mmu = ptdev->mmu;
 	struct panthor_vm *vm = ptdev->mmu->as.slots[as_nr].vm;
@@ -645,12 +644,6 @@ static int panthor_mmu_as_disable(struct panthor_device *ptdev, u32 as_nr,
 			return ret;
 	}
 
-	/* If the slot is going to be used immediately, don't bother changing
-	 * the config.
-	 */
-	if (recycle_slot)
-		return 0;
-
 	gpu_write64(mmu->iomem, AS_TRANSTAB(as_nr), 0);
 	gpu_write64(mmu->iomem, AS_MEMATTR(as_nr), 0);
 	gpu_write64(mmu->iomem, AS_TRANSCFG(as_nr), AS_TRANSCFG_ADRMODE_UNMAPPED);
@@ -777,7 +770,7 @@ int panthor_vm_active(struct panthor_vm *vm)
 		drm_WARN_ON(&ptdev->base, refcount_read(&lru_vm->as.active_cnt));
 		as = lru_vm->as.id;
 
-		ret = panthor_mmu_as_disable(ptdev, as, true);
+		ret = panthor_mmu_as_disable(ptdev, as);
 		if (ret)
 			goto out_unlock;
 
@@ -919,7 +912,7 @@ static void panthor_vm_declare_unusable(struct panthor_vm *vm)
 	vm->unusable = true;
 	mutex_lock(&ptdev->mmu->as.slots_lock);
 	if (vm->as.id >= 0 && drm_dev_enter(&ptdev->base, &cookie)) {
-		panthor_mmu_as_disable(ptdev, vm->as.id, false);
+		panthor_mmu_as_disable(ptdev, vm->as.id);
 		drm_dev_exit(cookie);
 	}
 	mutex_unlock(&ptdev->mmu->as.slots_lock);
@@ -1911,7 +1904,7 @@ static void panthor_mmu_irq_handler(struct panthor_device *ptdev, u32 status)
 			ptdev->mmu->as.slots[as].vm->unhandled_fault = true;
 
 		/* Disable the MMU to kill jobs on this AS. */
-		panthor_mmu_as_disable(ptdev, as, false);
+		panthor_mmu_as_disable(ptdev, as);
 		mutex_unlock(&ptdev->mmu->as.slots_lock);
 
 		status &= ~mask;
@@ -1940,7 +1933,7 @@ void panthor_mmu_suspend(struct panthor_device *ptdev)
 
 		if (vm) {
 			drm_WARN_ON(&ptdev->base,
-				    panthor_mmu_as_disable(ptdev, i, false));
+				    panthor_mmu_as_disable(ptdev, i));
 			panthor_vm_release_as_locked(vm);
 		}
 	}
@@ -2065,7 +2058,7 @@ static void panthor_vm_free(struct drm_gpuvm *gpuvm)
 		int cookie;
 
 		if (drm_dev_enter(&ptdev->base, &cookie)) {
-			panthor_mmu_as_disable(ptdev, vm->as.id, false);
+			panthor_mmu_as_disable(ptdev, vm->as.id);
 			drm_dev_exit(cookie);
 		}
 
@@ -3360,7 +3353,7 @@ void panthor_mmu_unplug(struct panthor_device *ptdev)
 
 		if (vm) {
 			drm_WARN_ON(&ptdev->base,
-				    panthor_mmu_as_disable(ptdev, i, false));
+				    panthor_mmu_as_disable(ptdev, i));
 			panthor_vm_release_as_locked(vm);
 		}
 	}

-- 
2.55.0