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mmc: alcor: fix DMA reads

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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: c5413ad815 ("mmc: add new Alcor Micro Cardreader SD/MMC driver")
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
This commit is contained in:
Daniel Drake 2019-03-20 14:36:53 +08:00 committed by Ulf Hansson
parent 031d2ccc16
commit 5ea47691bd
1 changed files with 19 additions and 6 deletions
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25
drivers/mmc/host/alcor.c
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@ -1044,14 +1044,27 @@ static void alcor_init_mmc(struct alcor_sdmmc_host *host)
mmc->caps2 = MMC_CAP2_NO_SDIO; mmc->caps2 = MMC_CAP2_NO_SDIO;
mmc->ops = &alcor_sdc_ops; 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_segs = AU6601_MAX_DMA_SEGMENTS;
mmc->max_seg_size = AU6601_MAX_DMA_BLOCK_SIZE; mmc->max_seg_size = AU6601_MAX_DMA_BLOCK_SIZE;
mmc->max_req_size = mmc->max_seg_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;
} }
static int alcor_pci_sdmmc_drv_probe(struct platform_device *pdev) static int alcor_pci_sdmmc_drv_probe(struct platform_device *pdev)