mmc: tmio_mmc: fix PIO fallback on DMA descriptor allocation failure

The easiest way to fall back to PIO, when a DMA descriptor allocation
fails is to disable DMA on the controller but continue with the current
request in PIO mode. This way tmio_mmc_start_dma() can become void, since
it cannot be failing any more. The current version is also broken: it is
testing a wrong pointer and thus failing to recognise, that a descriptor
allocation wasn't successful.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Chris Ball <cjb@laptop.org>

2 files changed, 25 insertions, 46 deletions

diff --git a/drivers/mmc/host/tmio_mmc.c b/drivers/mmc/host/tmio_mmc.c
index 4e75799291ca..63115a6de935 100644
--- a/drivers/mmc/host/tmio_mmc.c
+++ b/drivers/mmc/host/tmio_mmc.c
@@ -427,11 +427,12 @@ static void tmio_dma_complete(void *arg)
                 enable_mmc_irqs(host, TMIO_STAT_DATAEND);
 }
 
-static int tmio_mmc_start_dma_rx(struct tmio_mmc_host *host)
+static void tmio_mmc_start_dma_rx(struct tmio_mmc_host *host)
 {
         struct scatterlist *sg = host->sg_ptr;
         struct dma_async_tx_descriptor *desc = NULL;
         struct dma_chan *chan = host->chan_rx;
+        dma_cookie_t cookie;
         int ret;
 
         ret = dma_map_sg(&host->pdev->dev, sg, host->sg_len, DMA_FROM_DEVICE);
@@ -442,21 +443,20 @@ static int tmio_mmc_start_dma_rx(struct tmio_mmc_host *host)
         }
 
         if (desc) {
-                host->desc = desc;
                 desc->callback = tmio_dma_complete;
                 desc->callback_param = host;
-                host->cookie = desc->tx_submit(desc);
-                if (host->cookie < 0) {
-                        host->desc = NULL;
-                        ret = host->cookie;
+                cookie = desc->tx_submit(desc);
+                if (cookie < 0) {
+                        desc = NULL;
+                        ret = cookie;
                 } else {
                         chan->device->device_issue_pending(chan);
                 }
         }
         dev_dbg(&host->pdev->dev, "%s(): mapped %d -> %d, cookie %d, rq %p\n",
-                __func__, host->sg_len, ret, host->cookie, host->mrq);
+                __func__, host->sg_len, ret, cookie, host->mrq);
 
-        if (!host->desc) {
+        if (!desc) {
                 /* DMA failed, fall back to PIO */
                 if (ret >= 0)
                         ret = -EIO;
@@ -471,23 +471,18 @@ static int tmio_mmc_start_dma_rx(struct tmio_mmc_host *host)
                 dev_warn(&host->pdev->dev,
                          "DMA failed: %d, falling back to PIO\n", ret);
                 tmio_mmc_enable_dma(host, false);
-                reset(host);
-                /* Fail this request, let above layers recover */
-                host->mrq->cmd->error = ret;
-                tmio_mmc_finish_request(host);
         }
 
         dev_dbg(&host->pdev->dev, "%s(): desc %p, cookie %d, sg[%d]\n", __func__,
-                desc, host->cookie, host->sg_len);
-
-        return ret > 0 ? 0 : ret;
+                desc, cookie, host->sg_len);
 }
 
-static int tmio_mmc_start_dma_tx(struct tmio_mmc_host *host)
+static void tmio_mmc_start_dma_tx(struct tmio_mmc_host *host)
 {
         struct scatterlist *sg = host->sg_ptr;
         struct dma_async_tx_descriptor *desc = NULL;
         struct dma_chan *chan = host->chan_tx;
+        dma_cookie_t cookie;
         int ret;
 
         ret = dma_map_sg(&host->pdev->dev, sg, host->sg_len, DMA_TO_DEVICE);
@@ -498,19 +493,18 @@ static int tmio_mmc_start_dma_tx(struct tmio_mmc_host *host)
         }
 
         if (desc) {
-                host->desc = desc;
                 desc->callback = tmio_dma_complete;
                 desc->callback_param = host;
-                host->cookie = desc->tx_submit(desc);
-                if (host->cookie < 0) {
-                        host->desc = NULL;
-                        ret = host->cookie;
+                cookie = desc->tx_submit(desc);
+                if (cookie < 0) {
+                        desc = NULL;
+                        ret = cookie;
                 }
         }
         dev_dbg(&host->pdev->dev, "%s(): mapped %d -> %d, cookie %d, rq %p\n",
-                __func__, host->sg_len, ret, host->cookie, host->mrq);
+                __func__, host->sg_len, ret, cookie, host->mrq);
 
-        if (!host->desc) {
+        if (!desc) {
                 /* DMA failed, fall back to PIO */
                 if (ret >= 0)
                         ret = -EIO;
@@ -525,30 +519,22 @@ static int tmio_mmc_start_dma_tx(struct tmio_mmc_host *host)
                 dev_warn(&host->pdev->dev,
                          "DMA failed: %d, falling back to PIO\n", ret);
                 tmio_mmc_enable_dma(host, false);
-                reset(host);
-                /* Fail this request, let above layers recover */
-                host->mrq->cmd->error = ret;
-                tmio_mmc_finish_request(host);
         }
 
         dev_dbg(&host->pdev->dev, "%s(): desc %p, cookie %d\n", __func__,
-                desc, host->cookie);
-
-        return ret > 0 ? 0 : ret;
+                desc, cookie);
 }
 
-static int tmio_mmc_start_dma(struct tmio_mmc_host *host,
+static void tmio_mmc_start_dma(struct tmio_mmc_host *host,
                                struct mmc_data *data)
 {
         if (data->flags & MMC_DATA_READ) {
                 if (host->chan_rx)
-                        return tmio_mmc_start_dma_rx(host);
+                        tmio_mmc_start_dma_rx(host);
         } else {
                 if (host->chan_tx)
-                        return tmio_mmc_start_dma_tx(host);
+                        tmio_mmc_start_dma_tx(host);
         }
-
-        return 0;
 }
 
 static void tmio_issue_tasklet_fn(unsigned long priv)
@@ -584,9 +570,6 @@ static bool tmio_mmc_filter(struct dma_chan *chan, void *arg)
 static void tmio_mmc_request_dma(struct tmio_mmc_host *host,
                                  struct tmio_mmc_data *pdata)
 {
-        host->cookie = -EINVAL;
-        host->desc = NULL;
-
         /* We can only either use DMA for both Tx and Rx or not use it at all */
         if (pdata->dma) {
                 dma_cap_mask_t mask;
@@ -632,15 +615,11 @@ static void tmio_mmc_release_dma(struct tmio_mmc_host *host)
                 host->chan_rx = NULL;
                 dma_release_channel(chan);
         }
-
-        host->cookie = -EINVAL;
-        host->desc = NULL;
 }
 #else
-static int tmio_mmc_start_dma(struct tmio_mmc_host *host,
+static void tmio_mmc_start_dma(struct tmio_mmc_host *host,
                                struct mmc_data *data)
 {
-        return 0;
 }
 
 static void tmio_mmc_request_dma(struct tmio_mmc_host *host,
@@ -682,7 +661,9 @@ static int tmio_mmc_start_data(struct tmio_mmc_host *host,
         sd_ctrl_write16(host, CTL_SD_XFER_LEN, data->blksz);
         sd_ctrl_write16(host, CTL_XFER_BLK_COUNT, data->blocks);
 
-        return tmio_mmc_start_dma(host, data);
+        tmio_mmc_start_dma(host, data);
+
+        return 0;
 }
 
 /* Process requests from the MMC layer */
diff --git a/drivers/mmc/host/tmio_mmc.h b/drivers/mmc/host/tmio_mmc.h
index 0fedc78e3ea5..0b7d9162c1b5 100644
--- a/drivers/mmc/host/tmio_mmc.h
+++ b/drivers/mmc/host/tmio_mmc.h
@@ -112,9 +112,7 @@ struct tmio_mmc_host {
         struct tasklet_struct   dma_complete;
         struct tasklet_struct   dma_issue;
 #ifdef CONFIG_TMIO_MMC_DMA
-        struct dma_async_tx_descriptor *desc;
         unsigned int            dma_sglen;
-        dma_cookie_t            cookie;
 #endif
 };