How SPI can use DMA on Xavier!

Autonomous Machines Jetson & Embedded Systems Jetson AGX Xavier
1

HI ,
How SPI can use DMA?

3

The SPI driver default are using DMA for using the kernel SPI interface to transfer data.

5

Hi Shane, you mean if I use spy_sync or spi_async, I use the DMA to transfer data?

6

That is indeed what ShaneCCC was saying.

7

Thanks snarky. I mean, for example

00000427 struct spi_transfer {
00000428     /* it's ok if tx_buf == rx_buf (right?)
00000429      * for MicroWire, one buffer must be null
00000430      * buffers must work with dma_*map_single() calls, unless
00000431      *   spi_message.is_dma_mapped reports a pre-existing mapping
00000432      */
00000433     const void    *tx_buf;
00000434     void        *rx_buf;
00000435     unsigned    len;
00000436 
00000437     dma_addr_t    tx_dma;
00000438     dma_addr_t    rx_dma;
00000439 
00000440     unsigned    cs_change:1;
00000441     u8        bits_per_word;
00000442     u16        delay_usecs;
00000443     u32        speed_hz;
00000444 
00000445     struct list_head transfer_list;
00000446 };

if I create a transfer instence, when I use tx_dma, I use the DMA, if I use just tx_buf, I do not use the DMA, am I right?