What's the difference b/w __raw_readl/__raw_writel and readl/writel in linux kernel?

Question

What's the difference b/w __raw_readl/__raw_writel and readl/writel in linux kernel? It is said readl/writel is safer than __raw_readl/__raw_writel, then why do we still use __raw_readl/__raw_writel ?

Under what circumstances should we use this: __raw_readl/__raw_writel or readl/writel ?

Answer 1

It seems to be the case that

• raw denotes native byte ordering, non-raw means little-endian
• the __ prefix alternatives don't include memory barriers

See this LKML discussion and also the comments in linux/arch/arm/include/asm/io.h