On Wed, Sep 12, 2012 at 1:03 PM, Ville Syrjälä
<ville.syrjala@xxxxxxxxxxxxxxx> wrote:
> On Wed, Sep 12, 2012 at 12:35:01PM -0500, Rob Clark wrote:
>> On Wed, Sep 12, 2012 at 11:57 AM, Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx> wrote:
>> > On Sun, 9 Sep 2012 22:03:14 -0500
>> > Rob Clark <rob.clark@xxxxxxxxxx> wrote:
>> >
>> >> From: Rob Clark <rob@xxxxxx>
>> >>
>> >> The 'atomic' mechanism allows for multiple properties to be updated,
>> >> checked, and commited atomically. This will be the basis of atomic-
>> >> modeset and nuclear-pageflip.
>> >>
>> >> The basic flow is:
>> >>
>> >> state = dev->atomic_begin();
>> >> for (... one or more ...)
>> >> obj->set_property(obj, state, prop, value);
>> >> if (dev->atomic_check(state))
>> >> dev->atomic_commit(state, event);
>> >> dev->atomic_end(state);
>> >
>> > I think the above is more suited to drm_crtc_helper code. I think the
>> > top level callback should contain the arrays and be a single "multi
>> > flip" hook (or maybe a check then set double callback). For some
>> > drivers that'll end up being a lot simpler, rather than sprinkling
>> > atomic handling code in all the set_property callbacks.
>>
>> well, there are a few other places in drm_crtc.c where I want to use
>> the new API, to avoid drivers having to support both atomic API and
>> old set_plane/page_flip stuff.. the transactional API makes that a bit
>> easier, I think.. or at least I don't have to construct an array on
>> the stack.
>
> Usually you would need to build up the full state anyway before you can
> tell if it's good or bad. I don't see what some big array would buy here.
yup.. this was why I added drm_{crtc,plane,etc}_check_state(), to
bring back the common state checking that used to be done in the ioctl
fxns
>> > Having a transactional API just seems a little messier with both the
>> > atomic state and per-property state to track and rollback in the case
>> > of failure.
>>
>> For the rollback, I think I'm just going to move the array of property
>> values into drm_{crtc,plane,etc}_state. That way, userspace doesn't
>> see updated property values if they are not committed. It makes the
>> property value rollback automatic.
>
> This was my original idea as well. Separate the current and future
> states cleanly. At the moment it's all mixed up inside the objects
> somewhere. I sort of abandoned the idea so that I could avoid touching
> too much driver code while prototyping the atomic modesetting, but
> that's certainly the way I would design the system.
Yeah, I don't see any other way to do it sanely other than separating
out the current/future state. Fortunately for planes, there are only
a few drivers that support planes so it isn't too bad. For full
modesetting, it gets to be a lot of search and replace. But it makes
it so much cleaner so I think it is worth doing.
We could probably also simplify a bunch of the crtc helper code that
handles reverting to previous state.
BR,
-R
> --
> Ville Syrjälä
> Intel OTC
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