Then you can read and write to IO registers. It is just a more fancy way of calling write. This memory range belongs to the non-directly-mapped class of memory. First one does not seem to describe mmap at all. The word from the kernel developers, however, is that these functions are intended to be temporary driver-porting aids, and that they may go away in the future. In addition to write posting, on some large multiprocessing systems e.
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How to acess the physical address from linux kernel space? – Stack Overflow
Linux Device Drivers, Second Edition by Alessandro Rubini, Jonathan Corbet
Neither the reading nor the writing functions check the validity of addressbecause they are meant to be as fast as pointer dereferencing we already linud that sometimes they actually expand into pointer dereferencing.
As far as drivers are concerned, memory mapping can be implemented to provide user programs with direct access to device memory. In addition to write posting, on some large multiprocessing systems e. I think the best choice is to read through that ldd3 book There are also equivalents to memcpy.
Is there any possibility to access physical address without doing ioremap. Again, not mandatory but a good practice to follow. If you want to get joremap to the complete BAR without checking for its length first, pass 0 ljnux.
However, this situation is quite unlikely to happen. As a driver writer, however, you need not worry about how they work, as long as you use them.
Start by searching the kernel source for your distro Therefore, even though dereferencing a pointer works for now on the x86, failure to use the proper macros will hinder the portability and readability of the driver.
Then you can read and write to Ioremal registers. I suggest you look into the LDD3 bookit is free. Note the use of a write memory barrier here.
LINUX KERNEL INTERNALS: What is ioremap() ?
This kind of property cannot be hidden from driver writers in the API. Most architectures allocate new address space each time you call ioremapand they can run out unless you iotemap iounmap.
The discussion in this chapter touches mainly on ISA and PCI memory, while trying to convey general information as well. Hello, I’m developing a device driver for PCI device under kernel 3. No wonder you are confused.
ioremap() and memremap()
Navigation index next previous The Linux Kernel 4. Visit the following links: A driver author must issue a read from the same device to ensure that writes have occurred in the specific cases the author cares.
Whenever the program reads or writes in the assigned address range, it is actually accessing the device.
The returned virtual address is a current CPU mapping for the memory address given. Probing for ISA Memory.
Let me summarize, best to my abilities: It does explain ioremap in chapter 9, page