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

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Date:	Sat,  5 Jul 2014 06:56:28 +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] 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.

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 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 4c83445:

  Linux 3.16-rc3

are available in the git repository at:

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

-- 
1.7.10.4

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