Linux Device Drivers Development

__iomem cookie

__iomem is a kernel cookie used by Sparse, a semantic checker used by the kernel to find possible coding faults. To take advantage of the features offered by Sparse, it should be enabled at kernel compile time; if not, __iomem cookie will be ignored anyway.

The C=1 in the command line will enable Sparse for you, but Sparse should be installed first on your system:

sudo apt-get install sparse  

For example, when building a module, use:

make -C $KPATH M=$PWD C=1 modules

Alternatively, if the makefile is well-written, just type:

make C=1  

The following shows how __iomem is defined in the kernel:

#define __iomem    __attribute__((noderef, address_space(2))) 

It protects us from faulty drivers performing I/O memory access. Adding the ...