Re: [PATCH] cpu/hw_random cleanups

["H. Peter Anvin" <hpa@zytor.com>]

Jeff Garzik wrote:
> Here are the requested cleanups to cpu capabilities and hw_random.c.
> 
> For x86 experts, the new cpu cap words are what needs looking over.
> For example, I wonder if storing Intel's cpuid(0x00000001) ecx
> register output is wise on older Intel cpus.  I worry about garbage
> appearing there.  Is that a false worry?
> 

Yes; it should be completely safe.

> This has only been tested on Via Nehemiah CPUs...  I have a laptop with
> an Intel RNG on it at home, and will be testing with that later on
> tonight to make sure nothing is broken.  I'm hoping Alan or somebody can
> test AMD RNG... if not I'll poke around work and see if there are any
> boxes I can test on.
> 
> WRT hw_random, the main change there is to allow multiple independent
> openers to read(2) simultaneously, by removing the semaphore that
> limited userspace to a single open(2)er.
> 
> Comments welcome.  This patch is to be considered as a fourth patch in
> the previously-posted hw_random series.
> 
> 
> ===== arch/i386/kernel/cpu/centaur.c 1.7 vs edited =====
> --- 1.7/arch/i386/kernel/cpu/centaur.c	Tue Mar 11 21:35:40 2003
> +++ edited/arch/i386/kernel/cpu/centaur.c	Thu Mar 13 13:31:08 2003
> @@ -256,9 +256,10 @@
>  	if (cpuid_eax(0xC0000000) >= 0xC0000001) {
>  		set_bit(X86_FEATURE_CENTAUR_EFF, c->x86_capability);
>  

There is also no need to set a special feature bit for the existence of 
the feature flags.  If they are not present the additional capability 
word will simply be zero.