Re: Verify system io addresses

[linux-os]

On Fri, 28 Jan 2005 Jeff.Fellin@xxxxxxxxxxxx wrote:

> I want to develop a device driver that would allow access to board
> registers and memory that is addressable
> on the system bus.  The reason for this is to allow hardware developers to
> access board registers while the system
> is running to determine what is wrong with a board. The problem I'm having
> is attempting to determine if an address
> is addressable and would not cause a system panic when accessing. I'm
> looking for functions similar to the

> From within the kernel, on Intel machines, all addresses that are
mapped (using ioremap_nocache()) are addressable even if there is
no hardware at that address. It cannot cause a system panic. A
read from non-existent hardware will simply return a value with
all bits set (0xffffffff for a size_t). A write will go to
hyper-space, doing nothing.

> verify_access for user addresses, or if that is not available a method to
> determine that an address fault in the
> kernel is actually due to a bad board address being used.

There will be no such faults. You to use ioremap_nocache() first.
Remember to iounmap() when you are through.

> The driver has a user program that allows the hardware developers to peek
> and poke at address locations.
> So it is possible for them to mistype the address.
>
> Thank you in advance for your help.

If the access is through a port (in and out instructions), you
don't have to do anything, ports are always available in kernel
space.


BBBBUUUTTT!  If you write to somebody else's address-space like
a hard-disk controller, you can destroy all your data requiring
a complete re-installation of everything. That's why what you
want to do is NOT what you should do.

You need to have a competent programmer make a driver and
its attendant test-program to thoroughly test your board(s)
with no possibility of somebody entering wrong information.

> Jeff Fellin
> RFL Electronics
> Jeff.Fellin@xxxxxxxxxxxx
> 973 334-3100, x 327

Cheers,
Dick Johnson
Penguin : Linux version 2.6.10 on an i686 machine (5537.79 BogoMips).
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