Hi everyone, Thank for your time, I'm new to linux kernel. I am reading LDD3 chapter 15, Dirrect Memory Access section. I see that when I call function /dma_map_single/ and /dma_unmap_single/, I need to pass a direction as a parameter. I wonder what is purpose of it? Does It relate to something like permission? Can I call /dma_map_single /with DMA_BIDIRECTIONAL and then call /dma_unmap_single /with DMA_TO_DEVICE? Will it cause any problem? Thank you very much.
On Fri, 31 Aug 2018 08:53:29 +0800, "phind.uet@gmail.com" said:
Thank for your time, I'm new to linux kernel. I am reading LDD3 chapter 15, Dirrect Memory Access section. I see that when I call function /dma_map_single/ and /dma_unmap_single/, I need to pass a direction as a parameter.
Please note that the LDD is current as of 2.6.10, which is from 2005, and before git was used to maintain the kernel. [/usr/src/linux-next] git diff --shortstat v2.6.12 v4.19-rc1 70553 files changed, 23122660 insertions(+), 4318380 deletions(-) The *concepts* in LDD3 are still valid. However, the *exact* APIs are almost certainly changed by now. [/usr/src/linux-next] ls -l Documentation/DMA* -rw-r--r--. 1 source source 34951 Jul 18 2017 Documentation/DMA-API-HOWTO.txt -rw-rw-r--. 1 source source 28310 Sep 7 2017 Documentation/DMA-API.txt -rw-r--r--. 1 source source 5209 Jul 18 2017 Documentation/DMA-ISA-LPC.txt -rw-r--r--. 1 source source 7062 Jul 18 2017 Documentation/DMA-attributes.txt Start there.
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phind.uet＠gmail.com -
valdis.kletnieks＠vt.edu