[PATCH v2] drm: document how user-space should use link-status

[Simon Ser]

> > + *      When user-space performs an atomic commit on a connector with a "BAD"
> > + *      link-status without resetting the property to "GOOD", it gets
> > + *      implicitly reset. This might make the atomic commit fail if the modeset
> > + *      is unsuccessful.
>
> I think this was what Daniel was saying that the kernel should require
> ALLOW_MODESET to be set for the automatic reset, right?

Actually this paragraph isn't true. link-status is only reset to GOOD for
legacy modeset.

But right now this doesn't matter since no driver reads the link-status
property value as far as I can tell. Note, only i915 sets link-status
to BAD.

> I'm fine with how the doc is written now. But if ALLOW_MODESET becomes
> a requirement for the automatic reset, I suspect there is a risk to
> regress Weston, assuming the automatic reset used to be successful.

Right now a commit without ALLOW_MODESET won't reset link-status to GOOD,
but also won't re-train the link on i915. So I think it's fine to require
ALLOW_MODESET.

Should drivers read the value of the link-status property? Or should we
ignore user-space writes to the property and only require ALLOW_MODESET
to re-train the link?