diff options
| author | Daniel Drake <drake@endlessm.com> | 2019-03-20 14:36:53 +0800 |
|---|---|---|
| committer | Ulf Hansson <ulf.hansson@linaro.org> | 2019-03-21 11:19:06 +0100 |
| commit | 5ea47691bd99e1100707ec63364aff72324e2af4 (patch) | |
| tree | 027b2aff667b33417d9c63ba0bf38923b2f0ce2e /drivers | |
| parent | 031d2ccc16775c9531800979069e141fbedeb2f7 (diff) | |
mmc: alcor: fix DMA reads
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@mail.gmail.com
Signed-off-by: Daniel Drake <drake@endlessm.com>
Reviewed-by: Oleksij Rempel <linux@rempel-privat.de>
Fixes: c5413ad815a6 ("mmc: add new Alcor Micro Cardreader SD/MMC driver")
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/mmc/host/alcor.c | 25 |
1 files changed, 19 insertions, 6 deletions
diff --git a/drivers/mmc/host/alcor.c b/drivers/mmc/host/alcor.c index c712b7deb3a9..82a97866e0cf 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) |