[PATCH v2 10/17] drm/panthor: Check AS state before disabling

[Boris Brezillon <boris.brezillon@collabora.com>]

Use TRANSTAB == 0 as a way to detect if an AS slot is idle. This
allows us to make panthor_mmu_as_disable() a NOP when it's called
after a SOFT_RESET, which will be needed for our unplug rework.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
---
 drivers/gpu/drm/panthor/panthor_mmu.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
index 1b401fd0d2d7..a48466788f4d 100644
--- a/drivers/gpu/drm/panthor/panthor_mmu.c
+++ b/drivers/gpu/drm/panthor/panthor_mmu.c
@@ -634,6 +634,10 @@ static int panthor_mmu_as_disable(struct panthor_device *ptdev, u32 slot,
 
 	lockdep_assert_held(&ptdev->mmu->as.slots_lock);
 
+	/* The AS was disabled already, nothing to do. */
+	if (!gpu_read64(mmu->iomem, AS_TRANSTAB(slot)))
+		return 0;
+
 	panthor_mmu_irq_disable_events(&ptdev->mmu->irq,
 				       panthor_mmu_as_fault_mask(ptdev, slot));
 
@@ -656,11 +660,17 @@ static int panthor_mmu_as_disable(struct panthor_device *ptdev, u32 slot,
 	if (recycle_slot)
 		return 0;
 
-	gpu_write64(mmu->iomem, AS_TRANSTAB(slot), 0);
-	gpu_write64(mmu->iomem, AS_MEMATTR(slot), 0);
 	gpu_write64(mmu->iomem, AS_TRANSCFG(slot), AS_TRANSCFG_ADRMODE_UNMAPPED);
+	ret = as_send_cmd_and_wait(ptdev, slot, AS_COMMAND_UPDATE);
+	if (ret)
+		return ret;
 
-	return as_send_cmd_and_wait(ptdev, slot, AS_COMMAND_UPDATE);
+	/* We reset the other fields late to ensure that, if something fails,
+	 * the page table is considered active (TRANSTAB != NULL).
+	 */
+	gpu_write64(mmu->iomem, AS_MEMATTR(slot), 0);
+	gpu_write64(mmu->iomem, AS_TRANSTAB(slot), 0);
+	return 0;
 }
 
 static u32 panthor_mmu_fault_mask(struct panthor_device *ptdev, u32 value)

-- 
2.55.0