releases/5.0.5/mmc-alcor-fix-dma-reads.patch

   1 From 5ea47691bd99e1100707ec63364aff72324e2af4 Mon Sep 17 00:00:00 2001
   2 From: Daniel Drake <drake@endlessm.com>
   3 Date: Wed, 20 Mar 2019 14:36:53 +0800
   4 Subject: mmc: alcor: fix DMA reads
   5
   6 From: Daniel Drake <drake@endlessm.com>
   7
   8 commit 5ea47691bd99e1100707ec63364aff72324e2af4 upstream.
   9
  10 Setting max_blk_count to 1 here was causing the mmc block layer
  11 to always use the MMC_READ_SINGLE_BLOCK command here, which the
  12 driver does not DMA-accelerate.
  13
  14 Drop the max_blk_ settings here. The mmc host defaults suffice,
  15 along with the max_segs and max_seg_size settings, which I have
  16 now documented in more detail.
  17
  18 Now each MMC command reads 4 512-byte blocks, using DMA instead of
  19 PIO. On my SD card, this increases read performance (measured with dd)
  20 from 167kb/sec to 4.6mb/sec.
  21
  22 Link: http://lkml.kernel.org/r/CAD8Lp47L5T3jnAjBiPs1cQ+yFA3L6LJtgFvMETnBrY63-Zdi2g@mail.gmail.com
  23 Signed-off-by: Daniel Drake <drake@endlessm.com>
  24 Reviewed-by: Oleksij Rempel <linux@rempel-privat.de>
  25 Fixes: c5413ad815a6 ("mmc: add new Alcor Micro Cardreader SD/MMC driver")
  26 Cc: stable@vger.kernel.org
  27 Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
  28 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  29
  30 ---
  31  drivers/mmc/host/alcor.c |   25 +++++++++++++++++++------
  32  1 file changed, 19 insertions(+), 6 deletions(-)
  33
  34 --- a/drivers/mmc/host/alcor.c
  35 +++ b/drivers/mmc/host/alcor.c
  36 @@ -1044,14 +1044,27 @@ static void alcor_init_mmc(struct alcor_
  37         mmc->caps2 = MMC_CAP2_NO_SDIO;
  38         mmc->ops = &alcor_sdc_ops;
  39
  40 -       /* Hardware cannot do scatter lists */
  41 +       /* The hardware does DMA data transfer of 4096 bytes to/from a single
  42 +        * buffer address. Scatterlists are not supported, but upon DMA
  43 +        * completion (signalled via IRQ), the original vendor driver does
  44 +        * then immediately set up another DMA transfer of the next 4096
  45 +        * bytes.
  46 +        *
  47 +        * This means that we need to handle the I/O in 4096 byte chunks.
  48 +        * Lacking a way to limit the sglist entries to 4096 bytes, we instead
  49 +        * impose that only one segment is provided, with maximum size 4096,
  50 +        * which also happens to be the minimum size. This means that the
  51 +        * single-entry sglist handled by this driver can be handed directly
  52 +        * to the hardware, nice and simple.
  53 +        *
  54 +        * Unfortunately though, that means we only do 4096 bytes I/O per
  55 +        * MMC command. A future improvement would be to make the driver
  56 +        * accept sg lists and entries of any size, and simply iterate
  57 +        * through them 4096 bytes at a time.
  58 +        */
  59         mmc->max_segs = AU6601_MAX_DMA_SEGMENTS;
  60         mmc->max_seg_size = AU6601_MAX_DMA_BLOCK_SIZE;
  61 -
  62 -       mmc->max_blk_size = mmc->max_seg_size;
  63 -       mmc->max_blk_count = mmc->max_segs;
  64 -
  65 -       mmc->max_req_size = mmc->max_seg_size * mmc->max_segs;
  66 +       mmc->max_req_size = mmc->max_seg_size;
  67  }
  68
  69  static int alcor_pci_sdmmc_drv_probe(struct platform_device *pdev)