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

Ville Syrjälä ville.syrjala at
Fri Sep 30 15:45:09 UTC 2022

On Fri, Sep 30, 2022 at 06:37:00PM +0300, Pekka Paalanen wrote:
> 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?

Do you really want that for async flips? Async flips can't be
done atomically with anything else, so why are you even asking
the kernel to do that?

Ville Syrjälä

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