mmc: tmio: ensure end of DMA and SD access are in sync

The current code assumes that DMA is finished before SD access end is
flagged. Thus, it schedules the 'dma_complete' tasklet in the SD card
interrupt routine when DATAEND is set. The assumption is not safe,
though. Even by mounting an SD card, it can be seen that sometimes DMA
complete is first, sometimes DATAEND. It seems they are usually close
enough timewise to not cause problems. However, a customer reported that
with CMD53 sometimes things really break apart. As a result, the BSP has
a patch which introduces flags for both events and makes sure both flags
are set before scheduling the tasklet. The customer accepted the patch,
yet it doesn't seem a proper upstream solution to me.

This patch refactors the code to replace the tasklet with already
existing and more lightweight mechanisms. First of all, we set the
callback in a DMA descriptor to automatically get notified when DMA is
done. In the callback, we then use a completion to make sure the SD
access has already ended. Then, we proceed as before.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/tmio_mmc.h

@@ -137,7 +137,7 @@ struct tmio_mmc_host {
 	bool			force_pio;
 	struct dma_chan		*chan_rx;
 	struct dma_chan		*chan_tx;
-	struct tasklet_struct	dma_complete;
+	struct completion	dma_dataend;
 	struct tasklet_struct	dma_issue;
 	struct scatterlist	bounce_sg;
 	u8			*bounce_buf;

drivers/mmc/host/tmio_mmc_dma.c

@@ -43,6 +43,31 @@ void tmio_mmc_abort_dma(struct tmio_mmc_host *host)
 	tmio_mmc_enable_dma(host, true);
 }
 
+static void tmio_mmc_dma_callback(void *arg)
+{
+	struct tmio_mmc_host *host = arg;
+
+	wait_for_completion(&host->dma_dataend);
+
+	spin_lock_irq(&host->lock);
+
+	if (!host->data)
+		goto out;
+
+	if (host->data->flags & MMC_DATA_READ)
+		dma_unmap_sg(host->chan_rx->device->dev,
+			     host->sg_ptr, host->sg_len,
+			     DMA_FROM_DEVICE);
+	else
+		dma_unmap_sg(host->chan_tx->device->dev,
+			     host->sg_ptr, host->sg_len,
+			     DMA_TO_DEVICE);
+
+	tmio_mmc_do_data_irq(host);
+out:
+	spin_unlock_irq(&host->lock);
+}
+
 static void tmio_mmc_start_dma_rx(struct tmio_mmc_host *host)
 {
 	struct scatterlist *sg = host->sg_ptr, *sg_tmp;
@@ -88,6 +113,10 @@ static void tmio_mmc_start_dma_rx(struct tmio_mmc_host *host)
 			DMA_DEV_TO_MEM, DMA_CTRL_ACK);
 
 	if (desc) {
+		reinit_completion(&host->dma_dataend);
+		desc->callback = tmio_mmc_dma_callback;
+		desc->callback_param = host;
+
 		cookie = dmaengine_submit(desc);
 		if (cookie < 0) {
 			desc = NULL;
@@ -162,6 +191,10 @@ static void tmio_mmc_start_dma_tx(struct tmio_mmc_host *host)
 			DMA_MEM_TO_DEV, DMA_CTRL_ACK);
 
 	if (desc) {
+		reinit_completion(&host->dma_dataend);
+		desc->callback = tmio_mmc_dma_callback;
+		desc->callback_param = host;
+
 		cookie = dmaengine_submit(desc);
 		if (cookie < 0) {
 			desc = NULL;
@@ -221,29 +254,6 @@ static void tmio_mmc_issue_tasklet_fn(unsigned long priv)
 		dma_async_issue_pending(chan);
 }
 
-static void tmio_mmc_tasklet_fn(unsigned long arg)
-{
-	struct tmio_mmc_host *host = (struct tmio_mmc_host *)arg;
-
-	spin_lock_irq(&host->lock);
-
-	if (!host->data)
-		goto out;
-
-	if (host->data->flags & MMC_DATA_READ)
-		dma_unmap_sg(host->chan_rx->device->dev,
-			     host->sg_ptr, host->sg_len,
-			     DMA_FROM_DEVICE);
-	else
-		dma_unmap_sg(host->chan_tx->device->dev,
-			     host->sg_ptr, host->sg_len,
-			     DMA_TO_DEVICE);
-
-	tmio_mmc_do_data_irq(host);
-out:
-	spin_unlock_irq(&host->lock);
-}
-
 void tmio_mmc_request_dma(struct tmio_mmc_host *host, struct tmio_mmc_data *pdata)
 {
 	/* We can only either use DMA for both Tx and Rx or not use it at all */
@@ -306,7 +316,7 @@ void tmio_mmc_request_dma(struct tmio_mmc_host *host, struct tmio_mmc_data *pdat
 		if (!host->bounce_buf)
 			goto ebouncebuf;
 
-		tasklet_init(&host->dma_complete, tmio_mmc_tasklet_fn, (unsigned long)host);
+		init_completion(&host->dma_dataend);
 		tasklet_init(&host->dma_issue, tmio_mmc_issue_tasklet_fn, (unsigned long)host);
 	}
 

drivers/mmc/host/tmio_mmc_pio.c

@@ -596,11 +596,11 @@ static void tmio_mmc_data_irq(struct tmio_mmc_host *host, unsigned int stat)
 
 		if (done) {
 			tmio_mmc_disable_mmc_irqs(host, TMIO_STAT_DATAEND);
-			tasklet_schedule(&host->dma_complete);
+			complete(&host->dma_dataend);
 		}
 	} else if (host->chan_rx && (data->flags & MMC_DATA_READ) && !host->force_pio) {
 		tmio_mmc_disable_mmc_irqs(host, TMIO_STAT_DATAEND);
-		tasklet_schedule(&host->dma_complete);
+		complete(&host->dma_dataend);
 	} else {
 		tmio_mmc_do_data_irq(host);
 		tmio_mmc_disable_mmc_irqs(host, TMIO_MASK_READOP | TMIO_MASK_WRITEOP);