Re: [LIP] pci_alloc_consistent usage in x86-64 kernel

Hi Arun,

Thanks a lot for showing me what is wrong with me (have to read document 
completely :-( ).

Actually I dont know whether pci_map_single will be success always, thats 
the reason I have gone for pci_alloc_consistent.

Tell me which one of the following will be useful.
My device is capable of 64 bit DMA.

I thought of using get_free_pages and virt_to_bus pair together instead of 
pci_alloc_consistent will that be ok. or do i need to use pci_map_single 
before passing the address to my device.

Thanks Again.
Sathya




>From: Arun Sharma <[email protected]>
>Reply-To: linux-india-programmers-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
>To: linux-india-programmers-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
>Subject: Re: [LIP] pci_alloc_consistent usage in x86-64 kernel
>Date: Fri, 4 Jun 2004 00:42:36 -0700
>
>On Mon, May 31, 2004 at 03:53:24AM +0000, Sathya Prakash V wrote:
> > if (hwdev == NULL || hwdev->dma_mask < 0xffffffff || no_iommu)
> > 		gfp |= GFP_DMA;
> > If there is no_iommu then without considering the dma_mask the GFP_DMA 
>is
> > set and the memory allocation is limited.
>
>Sorry, I should've caught this in the first place. That is precisely
>what pci_alloc_consistent is defined to do.
>
>From Documentation/DMA-mapping.txt:
>
>The consistent DMA mapping interfaces, for non-NULL dev, will always
>return a DMA address which is SAC (Single Address Cycle) addressable.
>Even if the device indicates (via PCI dma mask) that it may address
>the upper 32-bits and thus perform DAC cycles, consistent allocation
>will still only return 32-bit PCI addresses for DMA.  This is true
>of the pci_pool interface as well.
>
>So, the real problem is: why are you using pci_alloc_consistent to
>allocate lots of memory and why not use the streaming DMA mapping APIs
>such as pci_map_single ?
>
>	-Arun
>
>
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