Messages in this thread | | | From | Masahiro Yamada <> | Date | Wed, 10 Oct 2018 21:00:01 +0900 | Subject | [DMA-engine Question] inconsistent policy of src_addr_widths, dst_addr_widths |
| |
Hi.
When I wrote my DMA engine driver, I had difficulty in understanding what to set to the struct dma_device members.
For example, src_addr_widths. I see two driver groups regarding this.
[A] BIT(DMA_SLAVE_BUSWIDTH_*_BYTES) are OR'ed
For example, st_fdma.c
https://github.com/torvalds/linux/blob/v4.19-rc4/drivers/dma/st_fdma.c#L729
[B] DMA_SLAVE_BUSWIDTH_*_BYTES are directly OR'ed without BIT()
For example, sh/rcar-dmac.c
https://github.com/torvalds/linux/blob/v4.19-rc4/drivers/dma/sh/rcar-dmac.c#L1778
Which is correct?
If we go with [A], BIT(DMA_SLAVE_BUSWIDTH_64_BYTES) i.e. BIT(64) would not fit in ddevice->src_addr_widths whose type is u32.
If we go with [B], the following formula is met. DMA_SLAVE_BUSWIDTH_3_BYTES == DMA_SLAVE_BUSWIDTH_1_BYTE | DMA_SLAVE_BUSWIDTH_2_BYTES
We never know whether 3_BYTES is supported, or it is just a combination of 1_BYTE and 2_BYTES.
-- Best Regards Masahiro Yamada
| |