drm/etnaviv: replace MMU flush marker with flush sequence

If a MMU is shared between multiple GPUs, all of them need to flush their
TLBs, so a single marker that gets reset on the first flush won't do.
Replace the flush marker with a sequence number, so that it's possible to
check if the TLB is in sync with the current page table state for each GPU.

Signed-off-by: Lucas Stach <[e-mail]>
Reviewed-by: Philipp Zabel <[e-mail]>
Reviewed-by: Guido Günther <[e-mail]>

drivers/gpu/drm/etnaviv/etnaviv_buffer.c

···
 	u32 return_target, return_dwords;
 	u32 link_target, link_dwords;
 	bool switch_context = gpu->exec_state != exec_state;
+	unsigned int new_flush_seq = READ_ONCE(gpu->mmu->flush_seq);
+	bool need_flush = gpu->flush_seq != new_flush_seq;
 
 	lockdep_assert_held(&gpu->lock);
 
···
 	 * need to append a mmu flush load state, followed by a new
 	 * link to this buffer - a total of four additional words.
 	 */
-	if (gpu->mmu->need_flush || switch_context) {
+	if (need_flush || switch_context) {
 		u32 target, extra_dwords;
 
 		/* link command */
 		extra_dwords = 1;
 
 		/* flush command */
-		if (gpu->mmu->need_flush) {
+		if (need_flush) {
 			if (gpu->mmu->version == ETNAVIV_IOMMU_V1)
 				extra_dwords += 1;
 			else
···
 
 		target = etnaviv_buffer_reserve(gpu, buffer, extra_dwords);
 
-		if (gpu->mmu->need_flush) {
+		if (need_flush) {
 			/* Add the MMU flush */
 			if (gpu->mmu->version == ETNAVIV_IOMMU_V1) {
 				CMD_LOAD_STATE(buffer, VIVS_GL_FLUSH_MMU,
···
 					SYNC_RECIPIENT_PE);
 			}
 
-			gpu->mmu->need_flush = false;
+			gpu->flush_seq = new_flush_seq;
 		}
 
 		if (switch_context) {

drivers/gpu/drm/etnaviv/etnaviv_gpu.h

···
 	int irq;
 
 	struct etnaviv_iommu *mmu;
+	unsigned int flush_seq;
 
 	/* Power Control: */
 	struct clk *clk_bus;

drivers/gpu/drm/etnaviv/etnaviv_mmu.c

···
 	}
 
 	list_add_tail(&mapping->mmu_node, &mmu->mappings);
-	mmu->need_flush = true;
+	mmu->flush_seq++;
 unlock:
 	mutex_unlock(&mmu->lock);
 
···
 		etnaviv_iommu_remove_mapping(mmu, mapping);
 
 	list_del(&mapping->mmu_node);
-	mmu->need_flush = true;
+	mmu->flush_seq++;
 	mutex_unlock(&mmu->lock);
 }
 
···
 			return ret;
 		}
 
-		mmu->need_flush = true;
+		mmu->flush_seq++;
 	}
 
 	list_add_tail(&mapping->mmu_node, &mmu->mappings);

drivers/gpu/drm/etnaviv/etnaviv_mmu.h

···
 	struct mutex lock;
 	struct list_head mappings;
 	struct drm_mm mm;
-	bool need_flush;
+	unsigned int flush_seq;
 };
 
 struct etnaviv_gem_object;