Subject: Doing DMA with the ide-driver

From: "Erik Niessen" <[email-masked]>
Date: Thu, 06 Jul 2000 02:28:24 CEST

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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From: Ralf Baechle <[email-masked]>
Date: Thu, 6 Jul 2000 03:25:10 +0200

> crash. Is this the solution???

What you're observing can be explained by caches not being flushed properly.
What kernel versions are you using?

  Ralf