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Force fixed dst addr for SDMA EIM on 4.1 with 6sl

Question asked by jayakumar2 on Nov 18, 2016
Latest reply on Nov 21, 2016 by igorpadykov


I'm using SDMA from host to EIM target (fpga) on i.mx6 sololite with Linux 4.1. I have it partially working now.

I'm using the following settings:

dma_cap_set(DMA_SLAVE, dma_m2m_mask);
m2m_dma_data.dma_request = 0;
m2m_dma_data.dma_request2 = 0;

m2m_dma_data.peripheral_type = IMX_DMATYPE_MEMORY

m2m_dma_data.priority = DMA_PRIO_HIGH;
dma_m2m_chan = dma_request_channel(dma_m2m_mask, dma_m2m_filter,

dma_m2m_config.direction = DMA_MEM_TO_MEM;
dma_m2m_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_2_BYTES;

dma_m2m_config.src_addr_width = DMA_SLAVE_BUSWIDTH_2_BYTES;
dma_m2m_config.src_maxburst = 128;
dma_m2m_config.dst_maxburst = 128;

dmaengine_slave_config(dma_m2m_chan, &dma_m2m_config);

dma_m2m_desc = dma_m2m_chan->device->device_prep_dma_memcpy(dma_m2m_chan, targetaddr, rbuf, bytecount, 0);


When I try this, eg:

targetaddr=0x0C000000 bytecount=4 sourcevalue=0xcccccccc

(2 writes of 16-bits width with value 0xcccccccc to address 0x0C000000)

Then this is detected correctly by the FPGA:
Read data=0xcccc


However, I noticed that the target address on the EIM bus is incrementing with each cycle. Meaning the first cycle on the bus has address 0 as expected, then the next cycle has address 0x02. So the last address becomes 0x02.


For my purpose with this FPGA, I need to treat the DMA as a fixed address. Meaning I don't want the destination address to increment automatically.


I tried changing the DMA_MEM_TO_MEM to DMA_MEM_TO_DEV. The result was no activity on the bus so it seems MEM_TO_DEV is not a valid option for an EIM target address.


I also tried changing IMX_DMATYPE_MEMORY to IMX_DMATYPE_FIFO_MEMORY and this also resulted in no activity on the bus.


I also checked that the device_prep_interleaved_dma dmaengine api function which has parameters for turning off dst_inc is not supported in imx-sdma. Linux/drivers/dma/imx-sdma.c - Linux Cross Reference - Free Electrons 


I'm a bit stuck. Anyone have any suggestions for a solution on imx6sl that would enable sdma to eim with non-incrementing targett address?