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Doing DMA with the ide-driver

To: linux-mips@oss.sgi.com
Subject: Doing DMA with the ide-driver
From: "Erik Niessen" <erik_niessen@hotmail.com>
Date: Thu, 06 Jul 2000 02:28:24 CEST
Sender: owner-linux-mips@oss.sgi.com
Hello,

I am trying to get an external ide-pci controller (CMD 646) working on an embedded mips board. The kernel-source is based on a 2.2.12 source tree.

The problem is doing DMA. I receive address (0x80ff0000) for my dmatable in the function ide_setup_dma (__get_free_pages). Then in ide_buildtable it sets up the dmatable. Address 0x80376000 and a count of 0x400 (check_partition reads 2 sectors from the harddrive). These are all virtual addresses. For setting up the dmatable I use physical addresses. On the embedded board there is a 1:1 map of i/o bus to main memory so platform_mem_iobus_base is 0.

So after doing the DMA read, I read only zero's at address 0x80376000 and the kernel hangs. But the harddrive is ready and I can't find any errors. It seems that it writes the data to a different memory location. After searching the memory the data is written at address 0x80000000?? Is the memory manager somewhere in between???

The next thing I did was reserving a piece of physical memory for DMA and fill in the dmatable myself. So that it uses my piece of reserved memory. After I did this, the data was at the correct address and the kernel didn't crash. Is this the solution???

Anyone a clue?

Thanks,

        Erik

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