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263c88ba GKH |
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) |