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DMA Bandwidth control T4240Qds rev 1

Question asked by Vigneshwaren Sankaran on Sep 13, 2014
Latest reply on Sep 19, 2014 by Yiping Wang

We are working on T4204QDS rev 1

We have a 10Gbps fibre optic card connected to Slot 7. The slot 7 is configured as x8 link with link speed 5GT/s (The card supports only link speed 5 GT/s and is x4 link width)


The bandwidth that I get from the card is around 2.5 Gbps (which is rather slow). I checked the Manual, and the manual says that DMA performs bandwidth control on the 8 channels.


Section in page 1988 says that bandwidth control can and should be disabled for getting higher performance.


How do I disable bandwidth control on my rev 1 board.



Using @luminliang 's suggestion, I checked the kernel code and found that in ./drivers/dma/fsldma.h the Bandwidth control variable was defined to be:

FSL_DMA_MR_BWC         0x08000000


This corresponds to a value of MRn[BWC] = "1000"

Is this the bottleneck for the 10Gbps card?

Would giving it a value of 0x0f000000 disable bandwidth control and therefore give me better performance?