Re: kmalloc with GFP_DMA, or get_free_pages!!!

Re: kmalloc with GFP_DMA, or get_free_pages!!!

[Jalajadevi Ganapathy]

I could not find that file in the Documentation directory.
I have one more question here. I read from a book that  virt_to_phy is same
as virt_to_bus for PCI devices. Is that True?


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Re: kmalloc with GFP_DMA, or get_free_pages!!!

[Jeff Garzik]

Jalajadevi Ganapathy wrote:
> 
> I could not find that file in the Documentation directory.

It's in kernel 2.4:
> [jgarzik@rum linux_2_4]$ ls -l Documentation/DM*
> -rw-r--r--    1 jgarzik  jgarzik     15302 Mar  7 04:00 Documentation/DMA-mapping.txt

> I have one more question here. I read from a book that  virt_to_phy is same
> as virt_to_bus for PCI devices. Is that True?

On some platforms yes, on some, no.  Nevertheless, in kernel 2.4.x at
least, do not use virt_to_bus and virt_to_phys, use DMA mapping... 
Using virt_to_bus will kill the link step on some platforms.

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Re: kmalloc with GFP_DMA, or get_free_pages!!!

[Jeff Garzik]

Jalajadevi Ganapathy wrote:
> 
> To allocate memory for DMA operations,

Use PCI DMA.  Yes, even for ISA devices.  Read
Documentation/DMA-mapping.txt.

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kmalloc with GFP_DMA, or get_free_pages!!!

[Jalajadevi Ganapathy]

To allocate memory for DMA operations, i can use kmalloc (,,GFP_DMA.. ). In
which case I need to use get_free_pages? Both the above gives me the
contiguous memory. I understand that get_free_pages gives me in terms of
pages. So it would be more than the memory which i asked for. I am not sure
watz the exact difference between these two.

Could anyone plz lemme know about this?

Thanks
Jalaja


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