bcm2835-mmc: Prevent DMA race condition

The end of a read operation is triggered by the completion of the DMA
transfer, but writes are complete when the data IRQ is raised. The
bcm2835-mmc driver contains a race between the handling of the DMA
completion interrupt and the submission of the next request. Fix the
race by deferring the completion of the request until the DMA
transfer finishes.

Signed-off-by: Phil Elwell <[email protected]>

Author: Phil Elwell

drivers/mmc/host/bcm2835-mmc.c

@@ -115,6 +115,7 @@ struct bcm2835_host {
 
 	bool					have_dma;
 	bool					use_dma;
+	bool					wait_for_dma;
 	/*end of DMA part*/
 
 	int						max_delay;	/* maximum length of time spent waiting */
@@ -341,6 +342,8 @@ static void bcm2835_mmc_dma_complete(void *param)
 
 	spin_lock_irqsave(&host->lock, flags);
 
+	host->use_dma = false;
+
 	if (host->data && !(host->data->flags & MMC_DATA_WRITE)) {
 		/* otherwise handled in SDHCI IRQ */
 		dma_chan = host->dma_chan_rxtx;
@@ -351,6 +354,9 @@ static void bcm2835_mmc_dma_complete(void *param)
 		     dir_data);
 
 		bcm2835_mmc_finish_data(host);
+	} else if (host->wait_for_dma) {
+		host->wait_for_dma = false;
+		tasklet_schedule(&host->finish_tasklet);
 	}
 
 	spin_unlock_irqrestore(&host->lock, flags);
@@ -690,6 +696,7 @@ void bcm2835_mmc_send_command(struct bcm2835_host *host, struct mmc_command *cmd
 	mod_timer(&host->timer, timeout);
 
 	host->cmd = cmd;
+	host->use_dma = false;
 
 	bcm2835_mmc_prepare_data(host, cmd);
 
@@ -759,8 +766,11 @@ static void bcm2835_mmc_finish_data(struct bcm2835_host *host)
 		}
 
 		bcm2835_mmc_send_command(host, data->stop);
-	} else
+	} else if (host->use_dma) {
+		host->wait_for_dma = true;
+	} else {
 		tasklet_schedule(&host->finish_tasklet);
+	}
 }
 
 static void bcm2835_mmc_finish_command(struct bcm2835_host *host)