Dma addr should use Kuseg1 for MIPS32?

Dma addr should use Kuseg1 for MIPS32?

[figo zhang]

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hi,

I am writing a driver for MIPS32. i wirte this code for DMA addr:

dma_vaddr =(char*) __get_free_pages(GFP_KERNEL|
GFP_DMA, order);
dma_phy = virt_to_phy(dma_vaddr);

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 .


Best,
Figo.zhang

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Re: Dma addr should use Kuseg1 for MIPS32?

[zhangfx]

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physical address (address comes out of the CPU bus to memory) can be 
different with bus address(used by DMA) in MIPS boards.

figo zhang 写道:
> hi,
>
> I am writing a driver for MIPS32. i wirte this code for DMA addr:
>
> dma_vaddr =(char*) __get_free_pages(GFP_KERNEL|GFP_DMA, order);
> dma_phy = virt_to_phy(dma_vaddr);
>
> 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 .
>
>
> Best,
> Figo.zhang

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Re: Dma addr should use Kuseg1 for MIPS32?

[Ralf Baechle]

On Mon, Dec 07, 2009 at 08:55:12PM +0800, figo zhang wrote:

> I am writing a driver for MIPS32. i wirte this code for DMA addr:
> 
> dma_vaddr =(char*) __get_free_pages(GFP_KERNEL|
> GFP_DMA, order);

You probably don't want to use GFP_DMA - unless your hardware has DMA
restrictions such as the ISA's bus's 16MB limit.

> dma_phy = virt_to_phy(dma_vaddr);

Ouch.  Don't.  See Documentation/DMA-API.txt for how to do it.

> 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.

  Ralf

Re: Dma addr should use Kuseg1 for MIPS32?

[figo zhang]

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2009/12/7 Ralf Baechle <ralf@linux-mips.org>

> On Mon, Dec 07, 2009 at 08:55:12PM +0800, figo zhang wrote:
>
> > I am writing a driver for MIPS32. i wirte this code for DMA addr:
> >
> > dma_vaddr =(char*) __get_free_pages(GFP_KERNEL|
> > GFP_DMA, order);
>
> You probably don't want to use GFP_DMA - unless your hardware has DMA
> restrictions such as the ISA's bus's 16MB limit.
>
> > dma_phy = virt_to_phy(dma_vaddr);
>

> Ouch.  Don't.  See Documentation/DMA-API.txt for how to do it.
>

hi Ralf,
is it using dma_alloc_coherent()? i see the this funtion in
arch/mips/mm/dma_default.c, it also invork the
__get_free_pages() and return the dma_addr by
plat_map_dma_mem()->virt_to_phy() , see
include/asm-mips/mach-genric/dma-coherent.h. so i think, i see use
__get_free_pages() alloce buffer for DMA.

>
> > 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?

2. If my system have HIGHMEM, so i alloc highmem pages by :
  page = alloc_pages(__GFP_HIGHMEM, order);
  phy = page_to_phys(page);

how i write this highmem phy addr to DMA base register?

Best,
Figo.zhang



>  Ralf
>

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Re: Dma addr should use Kuseg1 for MIPS32?

[Sergei Shtylyov]

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

Re: Dma addr should use Kuseg1 for MIPS32?

[figo zhang]

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2009/12/8 Sergei Shtylyov <sshtylyov@ru.mvista.com>

> 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.
>

I  write  0x1b00000 to my DMA Base register, the driver donot work.  write
(0x1b00000 | 0xa000000) it work, why?

>
> WBR, Sergei
>
>
>

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Re: Dma addr should use Kuseg1 for MIPS32?

[figo zhang]

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2009/12/8 figo zhang <figo1802@gmail.com>

>
>
> 2009/12/7 Ralf Baechle <ralf@linux-mips.org>
>
> On Mon, Dec 07, 2009 at 08:55:12PM +0800, figo zhang wrote:
>>
>> > I am writing a driver for MIPS32. i wirte this code for DMA addr:
>> >
>> > dma_vaddr =(char*) __get_free_pages(GFP_KERNEL|
>> > GFP_DMA, order);
>>
>> You probably don't want to use GFP_DMA - unless your hardware has DMA
>> restrictions such as the ISA's bus's 16MB limit.
>>
>> > dma_phy = virt_to_phy(dma_vaddr);
>>
>
>> Ouch.  Don't.  See Documentation/DMA-API.txt for how to do it.
>>
>
> hi Ralf,
> is it using dma_alloc_coherent()? i see the this funtion in
> arch/mips/mm/dma_default.c, it also invork the
> __get_free_pages() and return the dma_addr by
> plat_map_dma_mem()->virt_to_phy() , see
> include/asm-mips/mach-genric/dma-coherent.h. so i think, i see use
> __get_free_pages() alloce buffer for DMA.
>
>>
>> > 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?
>
> 2. If my system have HIGHMEM, so i alloc highmem pages by :
>   page = alloc_pages(__GFP_HIGHMEM, order);
>   phy = page_to_phys(page);
>
> how i write this highmem phy addr to DMA base register?
>

hi all,
 is anbody who would like to give me some advise about it?

Thanks,
Figo.zhang

>
> Best,
> Figo.zhang
>
>
>
>>  Ralf
>>
>
>

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