confused about HID1 bits and G5

Greg Watson gwatson at
Fri Apr 30 01:05:56 EST 2004

As a firmware designed (LinuxBIOS), I would support this. Obviously
there are some things that the firmware has to do, like enable memory,
but the less reliance the o/s has on magic behavior the better. It
makes firmware design simpler and more reliable.


On 29/04/2004, at 7:54 AM, Chris Friesen wrote:

> Benjamin Herrenschmidt wrote:
>>> It appears that we're relying on the firmware to set up a lot of the
>>> bits in this register--is there
>>> any reason we aren't forcing particular values?
>> Forcing values in HIDs is BAD. The firmware may set/clear bits to work
>> around specific CPU or north bridge bugs for example. That's why I
>> need
>> to change the code that force-clear HID4/5 one of these days too and
>> instead just clear the bits I want to be cleared.
> I'm just thinking of stuff that should really be set, like enabling
> the icache or the branch history
> table.  Do we really want to rely on firmware to do that? [1]
> Currently there are a bunch of bits in HID1 that are not specifically
> set in the linux code.  I
> think they should be set, but I have no way of actually checking the
> value since I'm running in
> 32-bit mode. [2]
> Chris
> 1. We've seen at least one firmware that didn't do this for some 74xx
> hardware.  Drove us nuts
> trying to figure out why performance wasn't meeting projections.
> 2. I'm trying to get a 64-bit toolchain built, but the gcc doesn't
> build when I follow the
> instructions on

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