Setting max_blk_count to 1 here was causing the mmc block layer to always use the MMC_READ_SINGLE_BLOCK command here, which the driver does not DMA-accelerate. Drop the max_blk_ settings here. The mmc host defaults suffice, along with the max_segs and max_seg_size settings, which I have now documented in more detail. Now each MMC command reads 4 512-byte blocks, using DMA instead of PIO. On my SD card, this increases read performance (measured with dd) from 167kb/sec to 4.6mb/sec. Link: http://lkml.kernel.org/r/CAD8Lp47L5T3jnAjBiPs1cQ+yFA3L6LJtgFvMETnBrY63-Zdi2g@xxxxxxxxxxxxxx Signed-off-by: Daniel Drake <drake@xxxxxxxxxxxx> --- drivers/mmc/host/alcor.c | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) diff --git a/drivers/mmc/host/alcor.c b/drivers/mmc/host/alcor.c index c712b7deb3a9d..82a97866e0cf4 100644 --- a/drivers/mmc/host/alcor.c +++ b/drivers/mmc/host/alcor.c @@ -1044,14 +1044,27 @@ static void alcor_init_mmc(struct alcor_sdmmc_host *host) mmc->caps2 = MMC_CAP2_NO_SDIO; mmc->ops = &alcor_sdc_ops; - /* Hardware cannot do scatter lists */ + /* 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. + */ mmc->max_segs = AU6601_MAX_DMA_SEGMENTS; mmc->max_seg_size = AU6601_MAX_DMA_BLOCK_SIZE; - - mmc->max_blk_size = mmc->max_seg_size; - mmc->max_blk_count = mmc->max_segs; - - mmc->max_req_size = mmc->max_seg_size * mmc->max_segs; + mmc->max_req_size = mmc->max_seg_size; } static int alcor_pci_sdmmc_drv_probe(struct platform_device *pdev) -- 2.19.1
