Re: DMA transfer with kiobuf, kernel 2.4.21

[sej <trash@aie-etudes.com>]

Hi,
thank you for your help.
I will read the DMA documentation. But I need to make DMA on User memory 
space allocated in user space. Because I don't want the kernel to make 
allocation and deallocation during execution for stability.
Best regards.
Sebastien


Arjan van de Ven wrote :

>On Tue, 2005-11-15 at 18:53 +0100, sej wrote:
>  
>
>>>that sounds the wrong approach.. why don't you make your device driver
>>>export an mmap function.. and let the userspace app use that ?
>>>      
>>>
>>I can't because I need to allocate 128MB of memory per PCI card and if I put for example 4 cards, I'll have 512MB in kernel memory, and I think there will be some problem in kernel.
>>    
>>
>
>no there isn't.. there is no rule that memory you allocate for this as
>to be lowmem... at all.
>
>  
>
>>
>>    
>>
>>>transfer->Descript[i].size        = PAGE_SIZE;
>>>transfer->Descript[i].pciaddr    = (ULONG)
>>>virt_to_phys(page_address(iobuf->maplist[idxIobuf]));
>>> 
>>>
>>>      
>>>
>>>you really need to use the PCI DMA mapping api!
>>>      
>>>
>>I have a plx bridge PCI9656 with a DMA controler. So I have to make a 
>>descriptor table with physical address and size.
>>I work in 32 bits address mode, but I don't know which function to call 
>>to get a 36bits address for my controler.
>>    
>>
>
>see the PCI DMA mapping api. the docs for it are in Documentation/
>
>
>
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