sdhci: let the controller wait for busy state to end

The sdhci controllers can interrupt us when the busy state from the
card has ended, saving CPU cycles and power.
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

drivers/mmc/host/sdhci.c

@@ -1266,9 +1266,31 @@ static void sdhci_cmd_irq(struct sdhci_host *host, u32 intmask)
 			SDHCI_INT_INDEX))
 		host->cmd->error = -EILSEQ;
 
-	if (host->cmd->error)
+	if (host->cmd->error) {
 		tasklet_schedule(&host->finish_tasklet);
-	else if (intmask & SDHCI_INT_RESPONSE)
+		return;
+	}
+
+	/*
+	 * The host can send and interrupt when the busy state has
+	 * ended, allowing us to wait without wasting CPU cycles.
+	 * Unfortunately this is overloaded on the "data complete"
+	 * interrupt, so we need to take some care when handling
+	 * it.
+	 *
+	 * Note: The 1.0 specification is a bit ambiguous about this
+	 *       feature so there might be some problems with older
+	 *       controllers.
+	 */
+	if (host->cmd->flags & MMC_RSP_BUSY) {
+		if (host->cmd->data)
+			DBG("Cannot wait for busy signal when also "
+				"doing a data transfer");
+		else
+			return;
+	}
+
+	if (intmask & SDHCI_INT_RESPONSE)
 		sdhci_finish_command(host);
 }
 
@@ -1278,11 +1300,16 @@ static void sdhci_data_irq(struct sdhci_host *host, u32 intmask)
 
 	if (!host->data) {
 		/*
-		 * A data end interrupt is sent together with the response
-		 * for the stop command.
+		 * The "data complete" interrupt is also used to
+		 * indicate that a busy state has ended. See comment
+		 * above in sdhci_cmd_irq().
 		 */
-		if (intmask & SDHCI_INT_DATA_END)
-			return;
+		if (host->cmd && (host->cmd->flags & MMC_RSP_BUSY)) {
+			if (intmask & SDHCI_INT_DATA_END) {
+				sdhci_finish_command(host);
+				return;
+			}
+		}
 
 		printk(KERN_ERR "%s: Got data interrupt 0x%08x even "
 			"though no data operation was in progress.\n",