Any memory access to either of those address ranges bypasses the MMU, and any access to one of those ranges bypasses the cache as well. Is there any possibility to access physical address without doing ioremap. However, this situation is quite unlikely to happen. Accesses to this space are provided through a set of functions which allow 8-bit, bit and bit accesses; also known as byte, word and long. This function does not give bus mappings for DMA transfers. The returned address is not guaranteed to be usable directly as a virtual address.

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By using our site, you acknowledge that llinux have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. PCI ordering rules also guarantee that PIO read responses arrive after any outstanding DMA writes from that bus, since for some devices the result of a readb call may signal to the driver that a DMA transaction is complete.

Linux Device Drivers, Second Edition by Alessandro Rubini, Jonathan Corbet

Hello, I’m developing a device driver for PCI device under kernel 3. Find More Posts by sundialsvcs. So a mapping must be set up first. If you need to reset your password, click here.

How to acess the physical address from linux kernel space? – Stack Overflow

The former is true, for example, of ISA devices, whose addresses are either burned in device logic circuits, statically assigned in local device memory, or set by means of physical jumpers. Any memory access to either of those address ranges bypasses the MMU, and any access to one of those ranges bypasses the cache as well. The above description all come from “makelinux”. So I put the iounmap in release method so that if the user will try to open gain the ioremap will be called.


To write code that will work across systems and kernel versions, however, you must avoid direct accesses and instead use the lnux functions. This function does not handle bus mappings for DMA transfers. Or it may be necessary simply to see if a device is present at a given address or not.

What is the right place for ioremap in device driver

The read and write functions are defined to be ordered. Sign up using Facebook. Visit the following links: I am working on rasberry pi board.

Sign up or log in Sign up using Google. The implementation will vary, however; on some they are ioreemap that expand to pointer operations, and on others they are real functions.

It does explain ioremap in chapter 9, page Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

It is only valid to use this function on addresses that have ioemap kernel mapping This function does not handle bus mappings for DMA transfers. I posted this also in Ubuntu community, hope I didn’t break any rules.


Neither the reading nor the writing functions check the validity of addressbecause they are meant to be as fast as pointer dereferencing we already know that sometimes they actually expand into pointer dereferencing. In the modern world, though, we must work with the virtual memory system and remap the memory range first. Note that registered members see fewer ads, and ContentLink is completely disabled once you log in.

If you’d like to contribute content, let us know. The quad-word nomenclature is a historical leftover from the times when all real processors had bit words. Post Your Answer Discard By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies. No wonder you are confused. Are you new to LinuxQuestions.

Di you know projects. The description of ioremap: I suggest you look into the LDD3 bookit is free.

ioremap() and memremap()

Remember, though, that these addresses should not be drvice directly; instead, functions like readb should be used. The ins and outs functions copy bytes, words or longs to the given port.

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