[PATCH 1/1] lib: sbi: relax scoldboot_lock spinlock

[Sean Anderson]

On 8/13/20 2:44 PM, Jessica Clarke wrote:
> On 13 Aug 2020, at 19:37, Jessica Clarke <jrtc27 at jrtc27.com> wrote:
>> On 13 Aug 2020, at 19:31, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>> Because there's global state to set up. You can't have all the other
>> harts rampaging through memory reading and writing whatever they like
>> until they can guarantee that the primary hart has performed all the
>> necessary initialisation for them to be able to roam free. I understand
>> you are trying to help and offer solutions, but it is getting rather
>> tedious to deal with what is now the third fundamentally broken patch
>> based on a lack of understanding, so please try to listen to us and
>> work with us to fix the problem you are facing rather than continuing
>> to play doctor and concoct your own broken "fixes".
> 
> Apologies, on closer inspection this does "fix" the problem as I had
> neglected the change to coldboot_lock's initialisation state. Yeah, it
> works, but, no, initialising a lock to be locked on boot is not good.
> All you've done is replace coldboot_done with !coldboot_lock (and made
> the latter play double-duty). This is hard to follow and just asking
> for mistakes to happen because it's not a normal thing to do.
> 
> Also, by doing this, you've now made all the harts busy-wait the entire
> time rather than be able to execute WFI until the primary hart is done,
> as they will be spinning for ages on the lock.

Why does this matter? This code will run for far less than a second,
once per boot. Any energy savings in OpenSBI will be trivial,
especially when compared to later boot stages.

--Sean