' bus_dmamap_load_mbuf_sg ( ) ' function usage problem

[tanniru.sankar at wipro.com]

 Hi Mark,

       Is it possible to allocate contigous memory of MJUM9BYTES ( 9K )
and  dmamap_load in one segment ? 
 
Thanks,
Sankar
 
              
 


-----Original Message-----
From: John-Mark Gurney [mailto:gurney_j at resnet.uoregon.edu] 
Sent: Tuesday, December 19, 2006 2:19 AM
To: Tanniru Sankar (WT01 - Computing Systems & Storage)
Cc: freebsd-net at freebsd.org
Subject: Re: ' bus_dmamap_load_mbuf_sg ( ) ' function usage problem

tanniru.sankar at wipro.com wrote this message on Mon, Dec 18, 2006 at
20:05 +0530:
>    I am facing a problem on FreeBSD 7.0 during mapping using '
> bus_dmamap_load_mbuf_sg ( ) ' function .
>    Details are below.
>  
>    It is AMD 64 bit machine. I have allocated jumbo buffer memory 
> using ' m_getcl ' function.
>  
>        mp = m_getjcl(M_DONTWAIT, MT_DATA, M_PKTHDR,  MJUM9BYTES);
>  
>     As it got success here, I am trying to map the buffer as below.
>         
>        err = bus_dmamap_load_mbuf_sg(dma_tag_rx, map, mp, &seg, &cnt, 
> BUS_DMA_NOWAIT);
>         
>       Here it is getting error for the mbuf size equal to  MJUM9BYTES.
> The type of error is ' EFBIG  '.
>    
>     I have create  rx jumbo dma tag with attributes as following.

[...]

>         MJUM9BYTES,       /* Maximum Size              */
> 
>         1 ,                           /* Number of Segments        */
> 
>         MJUM9BYTES,       /* Maximum Segment Size      */

This is probably the problem...  Most likely the buffer is
non-contiguous in memory, and needs 3 segments to satisfy the mapping...
Try increasing the number of segments and see what happens...

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."


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