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Date:   Tue, 08 Dec 2009 14:36:58 +0300
From:   Sergei Shtylyov <sshtylyov@ru.mvista.com>
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To:     figo zhang <figo1802@gmail.com>
Cc:     Ralf Baechle <ralf@linux-mips.org>,
        David Daney <ddaney@caviumnetworks.com>, macro@linux-mips.org,
        linux-mips@linux-mips.org
Subject: Re: Dma addr should use Kuseg1 for MIPS32?
References: <c6ed1ac50912070455n736af31fuf2c981fc182b494f@mail.gmail.com>         <20091207134502.GB5119@linux-mips.org> <c6ed1ac50912071749m49b1e5f5m7ae53384389338d9@mail.gmail.com>
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Hello.

figo zhang wrote:

>
>     > i write dma_phy to DMA base register, but why it cannot work? it
>     should
>     > write Kseg1 space to DMA register?
>     > I remember that it is ok for ARM/X86 .
>
>     It's only happens to work on some systems.
>
>
> in my puzzle, if i run 
> dma_vaddr =(char*) __get_free_pages(GFP_KERNEL,  order);
> dma_phy = virt_to_phy(dma_vaddr);
>
> if the result is:
> dma_vaddr = 0x801b00000;
> dma_phy = 0x1b00000;
>
> so i should write 0x1b00000 to my DMA Base register or wirte 
> (0x1b000000 | 0xa0000000) to DMA?

   You must always use the physical addresses when programming DMA, i.e. 
0x1b00000 in this case.

WBR, Sergei