Re: Socket buffer allocation outside DMA-able memory

[ashley jones <ashley_jones_2000@yahoo.com>]

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hi,
         I guess your 25 bit dma address field will be word alligned, so ur dma engine will be able to index up to 64 MB( 25+2 = 27 bits).
   
          If that is not the case then you can use one of the foll. work around,
   
    * dont give whole 64 MB to linux, give only Lower 32 MB.
    * Give only upper 32 MB to linux, and give memory to ur dma engine from lower 32 MB, and once you recv any data you copy to skb and submit to linux. ( ofcourse your performance will get hit in this case.)
   
   
  Regards,
  A'Jones.
  

art <art@sigrand.ru> wrote:
  Hello all!
I work with ADM5120 chip. it has embedded switch.
Switch descriptor has 25-bit dma addres field - so addressible only
32Mb!
My system has 64Mb memory. But I have to set 32Mb to make it work!
I thought that setting DMA mask can help. So in
/arch/mips/adm5120/setup.c i make:

static struct platform_device adm5120hcd_device = {
.name = "adm5120-hcd",
.id = -1,
.dev = {
.dma_mask = &hcd_dmamask,
.coherent_dma_mask = 0x01ffffff,
},
.num_resources = ARRAY_SIZE(adm5120_hcd_resources),
.resource = adm5120_hcd_resources,
};
But It is wrong, because dev_alloc_skb dont know to which device it
allocates buffer!

How to tell kernel allocate skbuffers in less then 32Mb addrspace whet
system has 64Mb?

-- 
Best regards,
art mailto:art@sigrand.ru





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