linux-kernel - [PATCH v5] Use DMA for data transfers in JZ4740 MMC driver

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Date:	Fri, 18 Jul 2014 01:41:34 +0200
From:	Apelete Seketeli <apelete@...eteli.net>
To:	Chris Ball <chris@...ntf.net>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Wei Yongjun <yongjun_wei@...ndmicro.com.cn>,
	Alex Smith <alex.smith@...tec.com>,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	linux-mmc@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH v5] Use DMA for data transfers in JZ4740 MMC driver

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 v4:
  - prefix functions with jz4740_mmc_ instead of jz4740_ to keep
    consistency with the rest of the code,

  - test (host->sg_len == 0) instead of (host->sg_len < 0) after
    dma_map_sg() in jz4740_mmc_start_dma_transfer() according to
    dmaengine.txt instructions.

Changes since v3:
  - use DMA engine device instead of MMC device in dma_map_sg() and
    dma_unmap_sg() as the memory transfers will be performed by the
    DMA engine,

  - remove unnecessary mem_res == NULL check in jz4740_mmc_probe()
    since devm_ioremap_resource() handles the mem_res == NULL case and
    print a message,

  - added a check to host->use_dma in jz4740_mmc_remove() to avoid
    calling jz4740_release_dma_channels() unnecessarily.

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@...NanoNote:/# uptime              |   root@...NanoNote:/# 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@...NanoNote:/# uptime              |   root@...NanoNote:/# 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 transfers 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 1795cd9:

  Linux 3.16-rc5

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 |  174 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 166 insertions(+), 8 deletions(-)

-- 
1.7.10.4

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