[MMC] Fix race condition in MMCI write-path data channel.

There seems to be a hardware race condition in the data channel where
we could end up receiving IRQs for more data than we have available.
Fix this by disabling IRQs when we run out of data; if the device
really does want more data, we'll underrun and flag an error
upstream.

drivers/mmc/mmci.c

@@ -61,17 +61,12 @@ mmci_request_end(struct mmci_host *host, struct mmc_request *mrq)
 
 static void mmci_start_data(struct mmci_host *host, struct mmc_data *data)
 {
-	unsigned int datactrl, timeout;
+	unsigned int datactrl, timeout, irqmask;
 
 	DBG("%s: data: blksz %04x blks %04x flags %08x\n",
 	    host->mmc->host_name, 1 << data->blksz_bits, data->blocks,
 	    data->flags);
 
-	datactrl = MCI_DPSM_ENABLE | data->blksz_bits << 4;
-
-	if (data->flags & MMC_DATA_READ)
-		datactrl |= MCI_DPSM_DIRECTION;
-
 	host->data = data;
 	host->buffer = data->req->buffer;
 	host->size = data->blocks << data->blksz_bits;
@@ -83,7 +78,21 @@ static void mmci_start_data(struct mmci_host *host, struct mmc_data *data)
 
 	writel(timeout, host->base + MMCIDATATIMER);
 	writel(host->size, host->base + MMCIDATALENGTH);
+
+	datactrl = MCI_DPSM_ENABLE | data->blksz_bits << 4;
+	if (data->flags & MMC_DATA_READ) {
+		datactrl |= MCI_DPSM_DIRECTION;
+		irqmask = MCI_RXFIFOHALFFULLMASK;
+	} else {
+		/*
+		 * We don't actually need to include "FIFO empty" here
+		 * since its implicit in "FIFO half empty".
+		 */
+		irqmask = MCI_TXFIFOHALFEMPTYMASK;
+	}
+
 	writel(datactrl, host->base + MMCIDATACTRL);
+	writel(irqmask, host->base + MMCIMASK1);
 }
 
 static void
@@ -201,24 +210,32 @@ static irqreturn_t mmci_pio_irq(int irq, void *dev_id, struct pt_regs *regs)
 				readl(host->base + MMCIFIFO);
 			}
 		}
-		if (status & (MCI_TXFIFOEMPTY|MCI_TXFIFOHALFEMPTY)) {
-			int count = host->size;
-			if (count > MCI_FIFOHALFSIZE)
-				count = MCI_FIFOHALFSIZE;
-			if (count && host->buffer) {
+
+		/*
+		 * We only need to test the half-empty flag here - if
+		 * the FIFO is completely empty, then by definition
+		 * it is more than half empty.
+		 */
+		if (status & MCI_TXFIFOHALFEMPTY) {
+			unsigned int maxcnt = status & MCI_TXFIFOEMPTY ?
+					      MCI_FIFOSIZE : MCI_FIFOHALFSIZE;
+			unsigned int count = min(host->size, maxcnt);
+
 			writesl(host->base + MMCIFIFO, host->buffer, count >> 2);
+
 			host->buffer += count;
 			host->size -= count;
+
+			/*
+			 * If we run out of data, disable the data IRQs;
+			 * this prevents a race where the FIFO becomes
+			 * empty before the chip itself has disabled the
+			 * data path.
+			 */
 			if (host->size == 0)
-					host->buffer = NULL;
-			} else {
-				static int first = 1;
-				if (first) {
-					first = 0;
-					printk(KERN_ERR "MMCI: ran out of source data\n");
-				}
-			}
+				writel(0, base + MMCIMASK1);
 		}
+
 		ret = 1;
 	} while (status);
 
@@ -413,7 +430,6 @@ static int mmci_probe(struct amba_device *dev, void *id)
 		goto irq0_free;
 
 	writel(MCI_IRQENABLE, host->base + MMCIMASK0);
-	writel(MCI_TXFIFOHALFEMPTYMASK|MCI_RXFIFOHALFFULLMASK, host->base + MMCIMASK1);
 
 	amba_set_drvdata(dev, mmc);