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In linux kernel. I get a reg [phy_addr], and do ioremap(), get [vir_addr], when i want to get val of this reg, What's the difference between readl() and *?

u32 value;

phys_addr_t phy_addr = 0x12345678; // it is reg addr

void *vir_addr = ioremap(phy_addr, sizeof(u32));

val = readl(vir_addr);
val = *(u32 *)vir_addr;
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    Goal of readl() (and friends) is to ensure that access to a memory-mapped register is properly treated as an I/O operation rather than just a basic RAM access. Study makelinux.net/ldd3/chp-9-sect-1.shtml Commented Jan 19, 2024 at 4:52
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    One difference is that readw()/readl()/writew()/writel() and friends assume the hardware registers being accessed use little-endian byte order, and the functions convert the values to/from the CPU's native byte order. Commented Jan 19, 2024 at 16:52
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    @IanAbbott, not only, the readl() might take care about alignment, while * is violating that on some architectures. Commented Jan 19, 2024 at 17:00
  • Does this answer your question? What is the benefit of calling ioread functions when using memory mapped IO Commented Feb 9, 2024 at 0:09
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