[PATCH v3] Use DMA for data transfers in JZ4740 MMC driver

[Apelete Seketeli]

Hello,

MMC driver for JZ4740 SoC is currently relying on PIO mode only for
data transfers.

The patch that comes as a follow-up of this message allows the use of
DMA for data transfers.

Changes since v2:
  - declare sg_len member of struct jz4740_mmc_host as int instead of
    unsigned int.
Changes since v1:
  - remove blank line added by mistake in jz_mmc_prepare_data_transfer().

According to the following DMA vs PIO benchmarks there seems to be a
slight improvement in transfer speed with the Ben NanoNote booting
from SD card, while load average seems to be roughly on par:

* With DMA:

Test cases |             root@BenNanoNote:/# uptime              |   root@BenNanoNote:/# time zcat root/fedora-16.iso.gz > /dev/null && uptime
-----------|----------------------------------------------------------------------------------------------------------------------------------
Test run 1 | 00:20:55 up 1 min,  load average: 1.26, 0.42, 0.14  |  00:26:10 up 6 min,  load average: 2.89, 1.94, 0.89
Test run 2 | 00:30:22 up 1 min,  load average: 1.16, 0.38, 0.13  |  00:35:34 up 6 min,  load average: 2.68, 1.86, 0.85
Test run 3 | 00:39:56 up 1 min,  load average: 1.16, 0.38, 0.13  |  00:45:06 up 6 min,  load average: 2.57, 1.76, 0.81
-----------|----------------------------------------------------------------------------------------------------------------------------------
  Average  |             1 min,  load average: 1.19, 0.39, 0.13  |              6 min,  load average: 2.71, 1.85, 0.85


* With PIO:

Test cases |             root@BenNanoNote:/# uptime              |   root@BenNanoNote:/# time zcat root/fedora-16.iso.gz > /dev/null && uptime
----------------------------------------------------------------------------------------------------------------------------------------------
Test run 1 | 00:50:47 up 1 min,  load average: 1.42, 0.49, 0.17  |  00:56:52 up 7 min,  load average: 2.47, 2.00, 0.98
Test run 2 | 01:00:19 up 1 min,  load average: 1.21, 0.39, 0.14  |  01:06:29 up 7 min,  load average: 2.45, 1.96, 0.96
Test run 3 | 01:11:27 up 1 min,  load average: 1.15, 0.36, 0.12  |  01:17:33 up 7 min,  load average: 2.63, 2.01, 0.97
-----------|----------------------------------------------------------------------------------------------------------------------------------
  Average  |             1 min,  load average: 1.26, 0.41, 0.14  |              7 min,  load average: 2.52, 1.99, 0.97


DMA tranfers performance might be further improved with a latter patch
by taking advantage of the asynchronous request capability of the MMC
framework.

Changes were rebased on top of linux master branch, built and tested
successfully.

The following changes since commit cd3de83:

  Linux 3.16-rc4

are available in the git repository at:

  git://git.seketeli.net/~apelete/linux.git jz4740-mmc-dma

Apelete Seketeli (1):
  mmc: jz4740: add dma infrastructure for data transfers

 drivers/mmc/host/jz4740_mmc.c |  172 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 164 insertions(+), 8 deletions(-)

-- 
1.7.10.4

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