Re: [RFC] RNG rewrite...

[Jeff Garzik <jgarzik@pobox.com>]

H. Peter Anvin wrote:
> Followup to:  <20051016005341.GB5946@plexity.net>
> By author:    Deepak Saxena <dsaxena@plexity.net>
> In newsgroup: linux.dev.kernel
> 
>>It's a magic regsiter we just read/write and could be done in userspace.
>>I also took a look at MPC85xx and it has the same sort of interface but
>>also has an error interrupt capability. On second thought a class
>>interface is overkill b/c there will only be one RNG per system, so
>>I can just do something like watchdogs where we have a bunch of simple
>>drivers exposing the same interface. We could do it in user space but
>>then we have separate RNG implementations for  x86 and !x86 and I'd
>>rather not see that. Can we move the x86 code out to userspace and
>>just let the daemon eat the numbers directly from HW? We can mmap() 
>>PCI devices, but I don't know enough about x86 to say whether msr 
>>instructions can execute out of userspace (or if we want them to...).

> MSR instructions cannot execute out of userspace, but the MSR driver
> might be possible to use.  It's usually quite slow, however.

MSRs are used for setup, not for actual data.

Intel:  magic MMIO address (readb)
AMD:	magic PIO address (inl)
VIA:	CPU instruction ('xstore')

	Jeff