KMS atomic state sets, full vs. minimal (Re: [PATCH v3 0/6] Add support for atomic async page-flips)

Pekka Paalanen ppaalanen at
Fri Sep 30 15:37:00 UTC 2022

On Fri, 30 Sep 2022 18:09:55 +0300
Ville Syrjälä <ville.syrjala at> wrote:

> That would actively discourage people from even attempting the
> "just dump all the state into the ioctl" approach with async flips
> since even the props whose value isn't even changing would be rejected.

About that.

To me it looks like just a classic case of broken communication.

The kernel developers assume that of course userspace will minimize the
state set to only those properties that change, because...?

Userspace developers think that of course the kernel will optimize the
state set into minimal changes, because the kernel actually has the
authoritative knowledge of what the current state is, and the driver
actually knows which properties are costly and need to be optimized and
which ones don't matter. It has never even occurred to me that the
kernel would not compare next state to current state.

No-one ever documented any expectations, did they?

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