[v4,4/4] drm/omap: partial workaround for DRA7xx DMM errata i878

diff --git a/drivers/gpu/drm/omapdrm/omap_dmm_priv.h b/drivers/gpu/drm/omapdrm/omap_dmm_priv.h
index c2785cc98dc9..60bb3f9297bc 100644
--- a/drivers/gpu/drm/omapdrm/omap_dmm_priv.h
+++ b/drivers/gpu/drm/omapdrm/omap_dmm_priv.h
@@ -159,6 +159,7 @@  struct dmm_platform_data {
 
 struct dmm {
 	struct device *dev;
+	dma_addr_t phys_base;
 	void __iomem *base;
 	int irq;
 
@@ -189,6 +190,12 @@  struct dmm {
 	struct list_head alloc_head;
 
 	const struct dmm_platform_data *plat_data;
+
+	bool dmm_workaround;
+	spinlock_t wa_lock;
+	u32 *wa_dma_data;
+	dma_addr_t wa_dma_handle;
+	struct dma_chan *wa_dma_chan;
 };
 
 #endif
diff --git a/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c b/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c
index ef9a88c772ed..05723527bec4 100644
--- a/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c
+++ b/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c
@@ -18,6 +18,7 @@ 
 #include <linux/completion.h>
 #include <linux/delay.h>
 #include <linux/dma-mapping.h>
+#include <linux/dmaengine.h>
 #include <linux/errno.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
@@ -79,14 +80,138 @@  static const u32 reg[][4] = {
 			DMM_PAT_DESCR__2, DMM_PAT_DESCR__3},
 };
 
+static int dmm_dma_copy(struct dmm *dmm, dma_addr_t src, dma_addr_t dst)
+{
+	struct dma_device *dma_dev = dmm->wa_dma_chan->device;
+	struct dma_async_tx_descriptor *tx;
+	enum dma_status status;
+	dma_cookie_t cookie;
+
+	tx = dma_dev->device_prep_dma_memcpy(dmm->wa_dma_chan, dst, src, 4, 0);
+	if (!tx) {
+		dev_err(dmm->dev, "Failed to prepare DMA memcpy\n");
+		return -EIO;
+	}
+
+	cookie = tx->tx_submit(tx);
+	if (dma_submit_error(cookie)) {
+		dev_err(dmm->dev, "Failed to do DMA tx_submit\n");
+		return -EIO;
+	}
+
+	dma_async_issue_pending(dmm->wa_dma_chan);
+	status = dma_sync_wait(dmm->wa_dma_chan, cookie);
+	if (status != DMA_COMPLETE)
+		dev_err(dmm->dev, "i878 wa DMA copy failure\n");
+
+	dmaengine_terminate_all(dmm->wa_dma_chan);
+	return 0;
+}
+
+static u32 dmm_read_wa(struct dmm *dmm, u32 reg)
+{
+	dma_addr_t src, dst;
+	int r;
+
+	src = dmm->phys_base + reg;
+	dst = dmm->wa_dma_handle;
+
+	r = dmm_dma_copy(dmm, src, dst);
+	if (r) {
+		dev_err(dmm->dev, "sDMA read transfer timeout\n");
+		return readl(dmm->base + reg);
+	}
+
+	/*
+	 * As per i878 workaround, the DMA is used to access the DMM registers.
+	 * Make sure that the readl is not moved by the compiler or the CPU
+	 * earlier than the DMA finished writing the value to memory.
+	 */
+	rmb();
+	return readl(dmm->wa_dma_data);
+}
+
+static void dmm_write_wa(struct dmm *dmm, u32 val, u32 reg)
+{
+	dma_addr_t src, dst;
+	int r;
+
+	writel(val, dmm->wa_dma_data);
+	/*
+	 * As per i878 workaround, the DMA is used to access the DMM registers.
+	 * Make sure that the writel is not moved by the compiler or the CPU, so
+	 * the data will be in place before we start the DMA to do the actual
+	 * register write.
+	 */
+	wmb();
+
+	src = dmm->wa_dma_handle;
+	dst = dmm->phys_base + reg;
+
+	r = dmm_dma_copy(dmm, src, dst);
+	if (r) {
+		dev_err(dmm->dev, "sDMA write transfer timeout\n");
+		writel(val, dmm->base + reg);
+	}
+}
+
 static u32 dmm_read(struct dmm *dmm, u32 reg)
 {
-	return readl(dmm->base + reg);
+	if (dmm->dmm_workaround) {
+		u32 v;
+		unsigned long flags;
+
+		spin_lock_irqsave(&dmm->wa_lock, flags);
+		v = dmm_read_wa(dmm, reg);
+		spin_unlock_irqrestore(&dmm->wa_lock, flags);
+
+		return v;
+	} else {
+		return readl(dmm->base + reg);
+	}
 }
 
 static void dmm_write(struct dmm *dmm, u32 val, u32 reg)
 {
-	writel(val, dmm->base + reg);
+	if (dmm->dmm_workaround) {
+		unsigned long flags;
+
+		spin_lock_irqsave(&dmm->wa_lock, flags);
+		dmm_write_wa(dmm, val, reg);
+		spin_unlock_irqrestore(&dmm->wa_lock, flags);
+	} else {
+		writel(val, dmm->base + reg);
+	}
+}
+
+static int dmm_workaround_init(struct dmm *dmm)
+{
+	dma_cap_mask_t mask;
+
+	spin_lock_init(&dmm->wa_lock);
+
+	dmm->wa_dma_data = dma_alloc_coherent(dmm->dev,  sizeof(u32),
+					      &dmm->wa_dma_handle, GFP_KERNEL);
+	if (!dmm->wa_dma_data)
+		return -ENOMEM;
+
+	dma_cap_zero(mask);
+	dma_cap_set(DMA_MEMCPY, mask);
+
+	dmm->wa_dma_chan = dma_request_channel(mask, NULL, NULL);
+	if (!dmm->wa_dma_chan) {
+		dma_free_coherent(dmm->dev, 4, dmm->wa_dma_data, dmm->wa_dma_handle);
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+static void dmm_workaround_uninit(struct dmm *dmm)
+{
+	dma_release_channel(dmm->wa_dma_chan);
+
+	dma_free_coherent(dmm->dev, 4, dmm->wa_dma_data, dmm->wa_dma_handle);
 }
 
 /* simple allocator to grab next 16 byte aligned memory from txn */
@@ -636,6 +761,9 @@  static int omap_dmm_remove(struct platform_device *dev)
 		if (omap_dmm->dummy_page)
 			__free_page(omap_dmm->dummy_page);
 
+		if (omap_dmm->dmm_workaround)
+			dmm_workaround_uninit(omap_dmm);
+
 		iounmap(omap_dmm->base);
 		kfree(omap_dmm);
 		omap_dmm = NULL;
@@ -681,6 +809,7 @@  static int omap_dmm_probe(struct platform_device *dev)
 		goto fail;
 	}
 
+	omap_dmm->phys_base = mem->start;
 	omap_dmm->base = ioremap(mem->start, SZ_2K);
 
 	if (!omap_dmm->base) {
@@ -696,6 +825,22 @@  static int omap_dmm_probe(struct platform_device *dev)
 
 	omap_dmm->dev = &dev->dev;
 
+	if (of_machine_is_compatible("ti,dra7")) {
+		/*
+		 * DRA7 Errata i878 says that MPU should not be used to access
+		 * RAM and DMM at the same time. As it's not possible to prevent
+		 * MPU accessing RAM, we need to access DMM via a proxy.
+		 */
+		if (!dmm_workaround_init(omap_dmm)) {
+			omap_dmm->dmm_workaround = true;
+			dev_info(&dev->dev,
+				"workaround for errata i878 in use\n");
+		} else {
+			dev_warn(&dev->dev,
+				 "failed to initialize work-around for i878\n");
+		}
+	}
+
 	hwinfo = dmm_read(omap_dmm, DMM_PAT_HWINFO);
 	omap_dmm->num_engines = (hwinfo >> 24) & 0x1F;
 	omap_dmm->num_lut = (hwinfo >> 16) & 0x1F;