the cost of EXPORT_SYMBOL_GPL

[Greg KH]

On Wed, Jun 17, 2020 at 02:35:28PM +0200, Martin Kaiser wrote:
> Hello Greg and all,
> 
> Thus wrote Greg KH (greg at kroah.com):
> 
> > Please do not do that. There are valid kernel apis to grant access to
> > registers easily,
> 
> the most simple case would be a "reset reason" register within the
> chip's address space. A hand-crafted driver would ioremap the region and
> implement a sysfs show method that reads the register.

No, that's not what sysfs is for.  You would export this in the proper
way that "reset reason" expects.

> What do you recommend for providing read access to such a register
> via sysfs? Is this a job for the userspace I/O (UIO) subsystem?

If all you want is direct memory access to userspace for stuff like
this, what's wrong with /dev/mem ?

If you want access to memory and interrupts to do it all in userspace,
then yes, that's what UIO is for, use that please.

thanks,

greg k-h