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authorAndrew Lunn <andrew@lunn.ch>2014-11-12 23:10:08 +0100
committerUlf Hansson <ulf.hansson@linaro.org>2014-11-26 14:31:00 +0100
commit3c583f70a8e2feda03db77d2c8e9a41d302ac657 (patch)
tree50ff085de42363bf2e2d37ed910bfe3e1b988021 /Documentation
parenta26eba614afff0e39594101bcb73014a9a22fb33 (diff)
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mmc: mvsdio: Work around broken TX DMA
In order to use the mvsdio driver for sdio, it has been necessary to use a module parameter to disable DMA so to force PIO is used. It is then possible to use wireless LAN devices like mwifiex found on topkick and mirabox. However, accessing an MMC SD card does work with DMA. Investigation has shown that MMC block device accesses are always aligned to 64 byte boundaries, where as transfers from mwifiex are rarely more than word aligned. It has also been determined that card to host transfers work with DMA for SDIO devices, but host to card transfers with DMA have problems. This patch extends the current checks for buffers which are not word aligned or multiple of words. All host to card transfers which are not 64 byte aligned are now also performed via PIO. This should not affect the performance of SD cards, but allow sdio devices to work out of the box, and they are likely to be more efficient since DMA will be used for card to host transfers. Tested on mirabox for wifi via mwifiex Tested on 370 RD for file systems on an SD card. Signed-off-by: Andrew Lunn <andrew@lunn.ch> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
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