mmc: tmio: use PIO for short transfers

This patch allows transferring of some requests in PIO and some in DMA
mode and defaults to using DMA only for transfers longer than 8 bytes.
This is especially useful with SDIO, which can have lots of 2- and 4-byte
transfers, creating unnecessary high overhead, when executed in DMA.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

1 files changed, 23 insertions, 10 deletions

diff --git a/drivers/mmc/host/tmio_mmc.c b/drivers/mmc/host/tmio_mmc.c
index e88627b3337..32ab1452d97 100644
--- a/drivers/mmc/host/tmio_mmc.c
+++ b/drivers/mmc/host/tmio_mmc.c
@@ -100,6 +100,8 @@
                 TMIO_STAT_CARD_REMOVE | TMIO_STAT_CARD_INSERT)
 #define TMIO_MASK_IRQ     (TMIO_MASK_READOP | TMIO_MASK_WRITEOP | TMIO_MASK_CMD)
 
+#define TMIO_MIN_DMA_LEN 8
+
 #define enable_mmc_irqs(host, i) \
         do { \
                 u32 mask;\
@@ -147,6 +149,7 @@ struct tmio_mmc_host {
         struct platform_device *pdev;
 
         /* DMA support */
+        bool                    force_pio;
         struct dma_chan         *chan_rx;
         struct dma_chan         *chan_tx;
         struct tasklet_struct   dma_complete;
@@ -385,6 +388,7 @@ static void tmio_mmc_reset_work(struct work_struct *work)
         host->cmd = NULL;
         host->data = NULL;
         host->mrq = NULL;
+        host->force_pio = false;
 
         spin_unlock_irqrestore(&host->lock, flags);
 
@@ -404,6 +408,7 @@ tmio_mmc_finish_request(struct tmio_mmc_host *host)
         host->mrq = NULL;
         host->cmd = NULL;
         host->data = NULL;
+        host->force_pio = false;
 
         cancel_delayed_work(&host->delayed_reset_work);
 
@@ -485,7 +490,7 @@ static void tmio_mmc_pio_irq(struct tmio_mmc_host *host)
         unsigned int count;
         unsigned long flags;
 
-        if (host->chan_tx || host->chan_rx) {
+        if ((host->chan_tx || host->chan_rx) && !host->force_pio) {
                 pr_err("PIO IRQ in DMA mode!\n");
                 return;
         } else if (!data) {
@@ -551,15 +556,11 @@ static void tmio_mmc_do_data_irq(struct tmio_mmc_host *host)
          */
 
         if (data->flags & MMC_DATA_READ) {
-                if (!host->chan_rx)
-                        disable_mmc_irqs(host, TMIO_MASK_READOP);
-                else
+                if (host->chan_rx && !host->force_pio)
                         tmio_check_bounce_buffer(host);
                 dev_dbg(&host->pdev->dev, "Complete Rx request %p\n",
                         host->mrq);
         } else {
-                if (!host->chan_tx)
-                        disable_mmc_irqs(host, TMIO_MASK_WRITEOP);
                 dev_dbg(&host->pdev->dev, "Complete Tx request %p\n",
                         host->mrq);
         }
@@ -583,7 +584,7 @@ static void tmio_mmc_data_irq(struct tmio_mmc_host *host)
         if (!data)
                 goto out;
 
-        if (host->chan_tx && (data->flags & MMC_DATA_WRITE)) {
+        if (host->chan_tx && (data->flags & MMC_DATA_WRITE) && !host->force_pio) {
                 /*
                  * Has all data been written out yet? Testing on SuperH showed,
                  * that in most cases the first interrupt comes already with the
@@ -596,11 +597,12 @@ static void tmio_mmc_data_irq(struct tmio_mmc_host *host)
                         disable_mmc_irqs(host, TMIO_STAT_DATAEND);
                         tasklet_schedule(&host->dma_complete);
                 }
-        } else if (host->chan_rx && (data->flags & MMC_DATA_READ)) {
+        } else if (host->chan_rx && (data->flags & MMC_DATA_READ) && !host->force_pio) {
                 disable_mmc_irqs(host, TMIO_STAT_DATAEND);
                 tasklet_schedule(&host->dma_complete);
         } else {
                 tmio_mmc_do_data_irq(host);
+                disable_mmc_irqs(host, TMIO_MASK_READOP | TMIO_MASK_WRITEOP);
         }
 out:
         spin_unlock(&host->lock);
@@ -649,12 +651,12 @@ static void tmio_mmc_cmd_irq(struct tmio_mmc_host *host,
          */
         if (host->data && !cmd->error) {
                 if (host->data->flags & MMC_DATA_READ) {
-                        if (!host->chan_rx)
+                        if (host->force_pio || !host->chan_rx)
                                 enable_mmc_irqs(host, TMIO_MASK_READOP);
                         else
                                 tasklet_schedule(&host->dma_issue);
                 } else {
-                        if (!host->chan_tx)
+                        if (host->force_pio || !host->chan_tx)
                                 enable_mmc_irqs(host, TMIO_MASK_WRITEOP);
                         else
                                 tasklet_schedule(&host->dma_issue);
@@ -810,6 +812,11 @@ static void tmio_mmc_start_dma_rx(struct tmio_mmc_host *host)
                 goto pio;
         }
 
+        if (sg->length < TMIO_MIN_DMA_LEN) {
+                host->force_pio = true;
+                return;
+        }
+
         disable_mmc_irqs(host, TMIO_STAT_RXRDY);
 
         /* The only sg element can be unaligned, use our bounce buffer then */
@@ -878,6 +885,11 @@ static void tmio_mmc_start_dma_tx(struct tmio_mmc_host *host)
                 goto pio;
         }
 
+        if (sg->length < TMIO_MIN_DMA_LEN) {
+                host->force_pio = true;
+                return;
+        }
+
         disable_mmc_irqs(host, TMIO_STAT_TXRQ);
 
         /* The only sg element can be unaligned, use our bounce buffer then */
@@ -1119,6 +1131,7 @@ static void tmio_mmc_request(struct mmc_host *mmc, struct mmc_request *mrq)
 
 fail:
         host->mrq = NULL;
+        host->force_pio = false;
         mrq->cmd->error = ret;
         mmc_request_done(mmc, mrq);
 }