media: rkvdec: Restore iommu addresses on errors

On errors, the rkvdec chip self resets. This can clear the addresses
programmed in the iommu. This case is signaled by the
RKVDEC_SOFTRESET_RDY status bit.

Since the iommu framework does not have a restore functionality, and
as recommended by the iommu subsystem maintainers, this patch
restores the iommu programming by attaching and detaching an empty
domain, which will clear and restore the default domain.

Suggested-by: Detlev Casanova <detlev.casanova@collabora.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Tested-by: Detlev Casanova <detlev.casanova@collabora.com>
Reviewed-by: Detlev Casanova <detlev.casanova@collabora.com>

drivers/staging/media/rkvdec/rkvdec.c

@@ -11,6 +11,7 @@
 
 #include <linux/clk.h>
 #include <linux/interrupt.h>
+#include <linux/iommu.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
@@ -948,24 +949,42 @@ static void rkvdec_v4l2_cleanup(struct rkvdec_dev *rkvdec)
 	v4l2_device_unregister(&rkvdec->v4l2_dev);
 }
 
+static void rkvdec_iommu_restore(struct rkvdec_dev *rkvdec)
+{
+	if (rkvdec->empty_domain) {
+		/*
+		 * To rewrite mapping into the attached IOMMU core, attach a new empty domain that
+		 * will program an empty table, then detach it to restore the default domain and
+		 * all cached mappings.
+		 * This is safely done in this interrupt handler to make sure no memory get mapped
+		 * through the IOMMU while the empty domain is attached.
+		 */
+		iommu_attach_device(rkvdec->empty_domain, rkvdec->dev);
+		iommu_detach_device(rkvdec->empty_domain, rkvdec->dev);
+	}
+}
+
 static irqreturn_t rkvdec_irq_handler(int irq, void *priv)
 {
 	struct rkvdec_dev *rkvdec = priv;
+	struct rkvdec_ctx *ctx = v4l2_m2m_get_curr_priv(rkvdec->m2m_dev);
 	enum vb2_buffer_state state;
 	u32 status;
 
 	status = readl(rkvdec->regs + RKVDEC_REG_INTERRUPT);
-	state = (status & RKVDEC_RDY_STA) ?
-		VB2_BUF_STATE_DONE : VB2_BUF_STATE_ERROR;
-
 	writel(0, rkvdec->regs + RKVDEC_REG_INTERRUPT);
-	if (cancel_delayed_work(&rkvdec->watchdog_work)) {
-		struct rkvdec_ctx *ctx;
 
-		ctx = v4l2_m2m_get_curr_priv(rkvdec->m2m_dev);
-		rkvdec_job_finish(ctx, state);
+	if (status & RKVDEC_RDY_STA) {
+		state = VB2_BUF_STATE_DONE;
+	} else {
+		state = VB2_BUF_STATE_ERROR;
+		if (status & RKVDEC_SOFTRESET_RDY)
+			rkvdec_iommu_restore(rkvdec);
 	}
 
+	if (cancel_delayed_work(&rkvdec->watchdog_work))
+		rkvdec_job_finish(ctx, state);
+
 	return IRQ_HANDLED;
 }
 
@@ -1033,6 +1052,13 @@ static int rkvdec_probe(struct platform_device *pdev)
 		return ret;
 	}
 
+	if (iommu_get_domain_for_dev(&pdev->dev)) {
+		rkvdec->empty_domain = iommu_paging_domain_alloc(rkvdec->dev);
+
+		if (!rkvdec->empty_domain)
+			dev_warn(rkvdec->dev, "cannot alloc new empty domain\n");
+	}
+
 	vb2_dma_contig_set_max_seg_size(&pdev->dev, DMA_BIT_MASK(32));
 
 	irq = platform_get_irq(pdev, 0);
@@ -1072,6 +1098,9 @@ static void rkvdec_remove(struct platform_device *pdev)
 	rkvdec_v4l2_cleanup(rkvdec);
 	pm_runtime_disable(&pdev->dev);
 	pm_runtime_dont_use_autosuspend(&pdev->dev);
+
+	if (rkvdec->empty_domain)
+		iommu_domain_free(rkvdec->empty_domain);
 }
 
 #ifdef CONFIG_PM

drivers/staging/media/rkvdec/rkvdec.h

@@ -95,6 +95,7 @@ struct rkvdec_dev {
 	void __iomem *regs;
 	struct mutex vdev_lock; /* serializes ioctls */
 	struct delayed_work watchdog_work;
+	struct iommu_domain *empty_domain;
 };
 
 struct rkvdec_ctx {