[Intel-gfx] [PATCH v3] drm/i915/hdcp: Update CP as per the kernel internal state

[Jani Nikula]

On Mon, 20 Jan 2020, Ramalingam C <ramalingam.c at intel.com> wrote:
> hdcp->value is used to track the internal transistions during the link
> failure and re-establishing it. When ever kernel want to update the
> "content protection" we take the required locks and update the property
> state along with uevent.

My point is this: How many states does your state machine need?

Considering the tri-state content_protection and tri-state hdcp->value,
you have 9 possible states and 362880 transitions. Add the new flag from
this patch, and you have 18 possible states and 6e15 transitions.

Obviously you don't need or use that many states or transitions, but you
need the code to limit the states and the transitions. You need the
review to ensure any changes take into account all the possible states
and transitions.

I've already noted one possible scenario in the proposed patch where
stuff goes out of sync, and I don't know what's really going to happen.

---

So maybe I don't understand what the hdcp code does, but then maybe you
shouldn't ask me to have a look at it... ;) I'm trying to point out why
I think it's maybe difficult to understand, and why I think adding
another flag might make it more difficult to maintain.

BR,
Jani.

-- 
Jani Nikula, Intel Open Source Graphics Center