mmc: alcor: enable DMA transfer of large buffers

DMA on this hardware is limited to dealing with a single page at a
time. Previously, the driver was set up accordingly to request single-page
DMA buffers, however that had the effect of generating a large number
of small MMC requests for data I/O.

Improve the driver to accept scatter-gather DMA buffers of larger sizes.
Iterate through those buffers a page at a time.

Testing with dd, this increases write performance from 2mb/sec to
10mb/sec, and increases read performance from 4mb/sec to 14mb/sec.

Signed-off-by: Daniel Drake <drake@endlessm.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

diff --git a/drivers/mmc/host/alcor.c b/drivers/mmc/host/alcor.c
index 3e2efbf..ddcdab1 100644 (file)
--- a/drivers/mmc/host/alcor.c
+++ b/drivers/mmc/host/alcor.c
@@ -54,9 +54,9 @@ struct alcor_sdmmc_host {
        struct delayed_work timeout_work;
 
        struct sg_mapping_iter sg_miter;        /* SG state for PIO */
+       struct sg_dma_page_iter sg_diter;       /* SG state for DMA */
        struct scatterlist *sg;
        unsigned int blocks;            /* remaining PIO blocks */
-       int sg_count;
 
        u32                     irq_status_sd;
        unsigned char           cur_power_mode;
@@ -117,30 +117,19 @@ static void alcor_reset(struct alcor_sdmmc_host *host, u8 val)
        dev_err(host->dev, "%s: timeout\n", __func__);
 }
 
+/*
+ * Perform DMA I/O of a single page.
+ */
 static void alcor_data_set_dma(struct alcor_sdmmc_host *host)
 {
        struct alcor_pci_priv *priv = host->alcor_pci;
-       u32 addr;
-
-       if (!host->sg_count)
-               return;
+       dma_addr_t addr;
 
-       if (!host->sg) {
-               dev_err(host->dev, "have blocks, but no SG\n");
+       if (!__sg_page_iter_dma_next(&host->sg_diter))
                return;
-       }
 
-       if (!sg_dma_len(host->sg)) {
-               dev_err(host->dev, "DMA SG len == 0\n");
-               return;
-       }
-
-
-       addr = (u32)sg_dma_address(host->sg);
-
-       alcor_write32(priv, addr, AU6601_REG_SDMA_ADDR);
-       host->sg = sg_next(host->sg);
-       host->sg_count--;
+       addr = sg_page_iter_dma_address(&host->sg_diter);
+       alcor_write32(priv, (u32) addr, AU6601_REG_SDMA_ADDR);
 }
 
 static void alcor_trigger_data_transfer(struct alcor_sdmmc_host *host)
@@ -153,12 +142,29 @@ static void alcor_trigger_data_transfer(struct alcor_sdmmc_host *host)
                ctrl |= AU6601_DATA_WRITE;
 
        if (data->host_cookie == COOKIE_MAPPED) {
+               /*
+                * For DMA transfers, this function is called just once,
+                * at the start of the operation. The hardware can only
+                * perform DMA I/O on a single page at a time, so here
+                * we kick off the transfer with the first page, and expect
+                * subsequent pages to be transferred upon IRQ events
+                * indicating that the single-page DMA was completed.
+                */
+               __sg_page_iter_start(&host->sg_diter.base, data->sg,
+                                    data->sg_len, 0);
+
                alcor_data_set_dma(host);
                ctrl |= AU6601_DATA_DMA_MODE;
                host->dma_on = 1;
-               alcor_write32(priv, data->sg_count * 0x1000,
+               alcor_write32(priv, data->blksz * data->blocks,
                               AU6601_REG_BLOCK_SIZE);
        } else {
+               /*
+                * For PIO transfers, we break down each operation
+                * into several sector-sized transfers. When one sector has
+                * complete, the IRQ handler will call this function again
+                * to kick off the transfer of the next sector.
+                */
                alcor_write32(priv, data->blksz, AU6601_REG_BLOCK_SIZE);
        }
 
@@ -233,9 +239,8 @@ static void alcor_prepare_data(struct alcor_sdmmc_host *host,
        host->data->bytes_xfered = 0;
        host->blocks = data->blocks;
        host->sg = data->sg;
-       host->sg_count = data->sg_count;
        dev_dbg(host->dev, "prepare DATA: sg %i, blocks: %i\n",
-                       host->sg_count, host->blocks);
+                       data->sg_count, host->blocks);
 
        if (data->host_cookie != COOKIE_MAPPED)
                alcor_prepare_sg_miter(host);
@@ -484,9 +489,6 @@ static int alcor_data_irq_done(struct alcor_sdmmc_host *host, u32 intmask)
                alcor_trf_block_pio(host, false);
                return 1;
        case AU6601_INT_DMA_END:
-               if (!host->sg_count)
-                       break;
-
                alcor_data_set_dma(host);
                break;
        default:
@@ -523,8 +525,7 @@ static void alcor_data_irq_thread(struct alcor_sdmmc_host *host, u32 intmask)
        if (alcor_data_irq_done(host, intmask))
                return;
 
-       if ((intmask & AU6601_INT_DATA_END) || !host->blocks ||
-           (host->dma_on && !host->sg_count))
+       if ((intmask & AU6601_INT_DATA_END) || !host->blocks || host->dma_on)
                alcor_finish_data(host);
 }
 
@@ -762,8 +763,7 @@ static void alcor_pre_req(struct mmc_host *mmc,
        struct alcor_sdmmc_host *host = mmc_priv(mmc);
        struct mmc_data *data = mrq->data;
        struct mmc_command *cmd = mrq->cmd;
-       struct scatterlist *sg;
-       unsigned int i, sg_len;
+       unsigned int sg_len;
 
        if (!data || !cmd)
                return;
@@ -785,11 +785,6 @@ static void alcor_pre_req(struct mmc_host *mmc,
        if (data->blksz & 3)
                return;
 
-       for_each_sg(data->sg, sg, data->sg_len, i) {
-               if (sg->length != AU6601_MAX_DMA_BLOCK_SIZE)
-                       return;
-       }
-
        /* This data might be unmapped at this time */
 
        sg_len = dma_map_sg(host->dev, data->sg, data->sg_len,
@@ -1037,26 +1032,13 @@ static void alcor_init_mmc(struct alcor_sdmmc_host *host)
        mmc->caps2 = MMC_CAP2_NO_SDIO;
        mmc->ops = &alcor_sdc_ops;
 
-       /* The hardware does DMA data transfer of 4096 bytes to/from a single
-        * buffer address. Scatterlists are not supported, but upon DMA
-        * completion (signalled via IRQ), the original vendor driver does
-        * then immediately set up another DMA transfer of the next 4096
-        * bytes.
-        *
-        * This means that we need to handle the I/O in 4096 byte chunks.
-        * Lacking a way to limit the sglist entries to 4096 bytes, we instead
-        * impose that only one segment is provided, with maximum size 4096,
-        * which also happens to be the minimum size. This means that the
-        * single-entry sglist handled by this driver can be handed directly
-        * to the hardware, nice and simple.
-        *
-        * Unfortunately though, that means we only do 4096 bytes I/O per
-        * MMC command. A future improvement would be to make the driver
-        * accept sg lists and entries of any size, and simply iterate
-        * through them 4096 bytes at a time.
+       /*
+        * Enable large requests through iteration of scatterlist pages.
+        * Limit to 240 sectors per request like the original vendor driver.
         */
-       mmc->max_segs = AU6601_MAX_DMA_SEGMENTS;
-       mmc->max_seg_size = AU6601_MAX_DMA_BLOCK_SIZE;
+       mmc->max_segs = 64;
+       mmc->max_seg_size = 240 * 512;
+       mmc->max_blk_count = 240;
        mmc->max_req_size = mmc->max_seg_size;
 }