440gx dma transfer with no data change at dest

Kevin Kleinosowski kevinko at arlut.utexas.edu
Wed Mar 8 08:16:08 EST 2006

I am running a simple test with a software initiated DMA transfer from one 
bigphysarea allocated buffer to another bigphysarea allocated buffer. 
The destination buffer shows no data changes once the transfer is done.

However, I perform the same simple test using __get_dma_pages() rather 
then the bigphysarea_alloc_pages() and the destination does get the 
data transfer.

Is there a reason this should fail for bigphysarea?  I understand the low 
memory addresses needed for the DMA controller on some platforms, but I 
didnt think that limitation existed on the PPC.  Besides that, the 
bigphysarea returns low memory address anyway.  Anyone have an idea why? 
An old archive email had someone with a similar problem, but there were no 
follow-ups to the message.

I have linux 2.4.27-pre3 patched, ppc-linux-gcc (GCC) 3.3.3 (DENX ELDK 
3.1.1 3.3.3-9), U-Boot 1.1.2, and GMS 440gx board.


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