Does s3cmci driver support DMA data transfer?
Lonsn at 163.com
Wed Jan 9 15:16:01 CET 2008
I'm now using s3cmci patch(http://svnweb.openmoko.org/branches/src/target/kernel/2.6.21.x/patches/s3c_mci.patch?rev=2805&view=auto) and it works well. The SD card write speed is about 26Mbits/s(S3C2440A 400MHz, Sandisk UltraIII 2GB sd card).
But the CPU load is too heavy(80%). So I want to let s3cmci driver work in DMA mode. I changed host->dodma = 1;
But it doesn't work and the driver cann't detect the sd card. Does anyone use the s3cmci driver in DMA mode successfully?
Another question: Can sd card work speed be more than 25MHz? As I know, the maximum sdi clock of S3C2440A is 33MHz(APB clock=67MHz, prescaler value=1) and UltraIII sd card can support 40MHz frequency(20MBytes/s). If we can let s3cmci driver works in 33MHz modes, maybe the sd card IO performance could be increased a lot. But the sdi clock works only 22.5MHz(prescaler value=2) mode now.
Thanks a lot
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