Re: [PATCH 4/5] drm/atomic: Make the drm_atomic_state documentation less ambiguous
On Fri, 8 Dec 2023 16:20:37 +0100 Maxime Ripard wrote: > On Fri, Dec 08, 2023 at 03:59:46PM +0200, Pekka Paalanen wrote: > > On Fri, 8 Dec 2023 13:25:22 +0100 > > Maxime Ripard wrote: > > > > > On Fri, Dec 08, 2023 at 10:08:28AM +0200, Pekka Paalanen wrote: > > > > On Thu, 7 Dec 2023 15:27:33 +0100 > > > > Maxime Ripard wrote: > > > > > > > > > On Tue, Dec 05, 2023 at 10:51:06AM +0200, Pekka Paalanen wrote: > > > > > > On Mon, 4 Dec 2023 13:17:06 +0100 > > > > > > Maxime Ripard wrote: > > > > > > > > > > > > > The current documentation of drm_atomic_state says that it's the > > > > > > > "global > > > > > > > state object". This is confusing since, while it does contain all > > > > > > > the > > > > > > > objects affected by an update and their respective states, if an > > > > > > > object > > > > > > > isn't affected by this update it won't be part of it. > > > > > > > > > > > > > > Thus, it's not truly a "global state", unlike object state > > > > > > > structures > > > > > > > that do contain the entire state of a given object. > > > > > > > > > > > > > > Signed-off-by: Maxime Ripard > > > > > > > --- > > > > > > > include/drm/drm_atomic.h | 10 +- > > > > > > > 1 file changed, 9 insertions(+), 1 deletion(-) ... > > Sima's phrasing is an addition, not a replacement, to this. There are > > two things: > > > > a) An atomic commit does not need to contain all the objects of a > >drm_device. > > > > b) An atomic commit may affect more objects than it originally > >contained. (from userspace perspective) > > > > Here b) is important for userspace to know, because it can be > > surprising, but I understand that this patch is not userspace doc. > > Right, so my initial goal from this series was to make sure the > ambiguous meaning of what a state was was (hopefully) lifted, and thus > we could progress on your userspace doc patch. So I want to address > point A here. > > B is also important, but maybe we should discuss it into a separate > patch? Sure! Just mind both cases to not accidentally imply something about b) when talking about a). Thanks, pq pgp4sm9233naR.pgp Description: OpenPGP digital signature
Re: [PATCH 4/5] drm/atomic: Make the drm_atomic_state documentation less ambiguous
On Fri, Dec 08, 2023 at 03:59:46PM +0200, Pekka Paalanen wrote:
> On Fri, 8 Dec 2023 13:25:22 +0100
> Maxime Ripard wrote:
>
> > On Fri, Dec 08, 2023 at 10:08:28AM +0200, Pekka Paalanen wrote:
> > > On Thu, 7 Dec 2023 15:27:33 +0100
> > > Maxime Ripard wrote:
> > >
> > > > On Tue, Dec 05, 2023 at 10:51:06AM +0200, Pekka Paalanen wrote:
> > > > > On Mon, 4 Dec 2023 13:17:06 +0100
> > > > > Maxime Ripard wrote:
> > > > >
> > > > > > The current documentation of drm_atomic_state says that it's the
> > > > > > "global
> > > > > > state object". This is confusing since, while it does contain all
> > > > > > the
> > > > > > objects affected by an update and their respective states, if an
> > > > > > object
> > > > > > isn't affected by this update it won't be part of it.
> > > > > >
> > > > > > Thus, it's not truly a "global state", unlike object state
> > > > > > structures
> > > > > > that do contain the entire state of a given object.
> > > > > >
> > > > > > Signed-off-by: Maxime Ripard
> > > > > > ---
> > > > > > include/drm/drm_atomic.h | 10 +-
> > > > > > 1 file changed, 9 insertions(+), 1 deletion(-)
> > > > > >
> > > > > > diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> > > > > > index 914574b58ae7..81ad7369b90d 100644
> > > > > > --- a/include/drm/drm_atomic.h
> > > > > > +++ b/include/drm/drm_atomic.h
> > > > > > @@ -346,11 +346,19 @@ struct __drm_private_objs_state {
> > > > > > };
> > > > > >
> > > > > > /**
> > > > > > - * struct drm_atomic_state - the global state object for atomic
> > > > > > updates
> > > > > > + * struct drm_atomic_state - Atomic Update structure
> > > > > > + *
> > > > > > + * This structure is the kernel counterpart of @drm_mode_atomic
> > > > > > and contains
> > > > > > + * all the objects affected by an atomic modeset update and their
> > > > > > states.
> > > > >
> > > > > Drop "modeset"? An update can be without a modeset.
> > > >
> > > > Yeah, good point
> > > >
> > > > > > *
> > > > > > * States are added to an atomic update by calling
> > > > > > drm_atomic_get_crtc_state(),
> > > > > > * drm_atomic_get_plane_state(), drm_atomic_get_connector_state(),
> > > > > > or for
> > > > > > * private state structures, drm_atomic_get_private_obj_state().
> > > > > > + *
> > > > > > + * NOTE: While this structure looks to be global and affecting the
> > > > > > whole DRM
> > > > > > + * device, it only contains the objects affected by the atomic
> > > > > > commit.
> > > > >
> > > > > This new phrasing is much more clear to me than the old one.
> > > >
> > > > Great
> > > >
> > > > > > + * Unaffected objects will not be part of that update, unless they
> > > > > > have been
> > > > > > + * explicitly added by either the framework or the driver.
> > > > >
> > > > > If the framework or a driver adds an object, then it's no longer
> > > > > unaffected, is it?
> > > >
> > > > I guess what I meant to say is that it's affected as a side effect that
> > > > the userspace cannot anticipate.
> > > >
> > > > The typical example being that changing a property on a connector would
> > > > need to pull the CRTC into the update to disable / enable the CRTC,
> > > > encoder and connector.
> > >
> > > Right, that's the easy case. This can even be documented and therefore
> > > become expected by userspace. The associations between CRTC and
> > > connector are published, e.g. the current routing.
> > >
> > > What I was thinking of was much more hidden:
> > >
> > > Userspace explicitly programs CRTC A and the connector connected to it.
> > > None of the mentioned KMS objects in that atomic commit refer to CRTC B
> > > in any way, not in old nor in new device state. Still, the driver
> > > decides to pull CRTC B in, because it needs to adjust something there
> > > (ISTR hearing "watermarks" in some conversation) in order to
> > > accommodate changes in CRTC A.
> > >
> > > So there are two categories of pulling in extra KMS objects: knowable
> > > and unknowable. Or expected and unexpected.
> > >
> > > If userspace changes things on a connector connected to CRTC A, you can
> > > expect to pull in CRTC A. That's knowable. If the driver unexpectedly
> > > also pulls in CRTC B while userspace made absolutely no explicit nor
> > > implicit reference to it, that's unknowable.
> >
> > > The unknowable/unexpected additions are very hardware and driver
> > > specific and not reliably determinable from an atomic commit UAPI
> > > structure.
> >
> > So I had a quick look at all the drivers we have in-tree, and it looks
> > to be either a plane or a connector pulling its CRTC in. I guess they
> > would all qualify as knowable.
>
> Yes.
>
> > For unknowable, yeah, it's kind of bad, but at the same time you have to
> > deal with the hardware you have. Like, for vc4 for example, there's a
> > single controller before the CRTCs that deals with the blending, scaling
> > and all the other
Re: [PATCH 4/5] drm/atomic: Make the drm_atomic_state documentation less ambiguous
On Fri, 8 Dec 2023 13:25:22 +0100
Maxime Ripard wrote:
> On Fri, Dec 08, 2023 at 10:08:28AM +0200, Pekka Paalanen wrote:
> > On Thu, 7 Dec 2023 15:27:33 +0100
> > Maxime Ripard wrote:
> >
> > > On Tue, Dec 05, 2023 at 10:51:06AM +0200, Pekka Paalanen wrote:
> > > > On Mon, 4 Dec 2023 13:17:06 +0100
> > > > Maxime Ripard wrote:
> > > >
> > > > > The current documentation of drm_atomic_state says that it's the
> > > > > "global
> > > > > state object". This is confusing since, while it does contain all the
> > > > > objects affected by an update and their respective states, if an
> > > > > object
> > > > > isn't affected by this update it won't be part of it.
> > > > >
> > > > > Thus, it's not truly a "global state", unlike object state structures
> > > > > that do contain the entire state of a given object.
> > > > >
> > > > > Signed-off-by: Maxime Ripard
> > > > > ---
> > > > > include/drm/drm_atomic.h | 10 +-
> > > > > 1 file changed, 9 insertions(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> > > > > index 914574b58ae7..81ad7369b90d 100644
> > > > > --- a/include/drm/drm_atomic.h
> > > > > +++ b/include/drm/drm_atomic.h
> > > > > @@ -346,11 +346,19 @@ struct __drm_private_objs_state {
> > > > > };
> > > > >
> > > > > /**
> > > > > - * struct drm_atomic_state - the global state object for atomic
> > > > > updates
> > > > > + * struct drm_atomic_state - Atomic Update structure
> > > > > + *
> > > > > + * This structure is the kernel counterpart of @drm_mode_atomic and
> > > > > contains
> > > > > + * all the objects affected by an atomic modeset update and their
> > > > > states.
> > > >
> > > > Drop "modeset"? An update can be without a modeset.
> > >
> > > Yeah, good point
> > >
> > > > > *
> > > > > * States are added to an atomic update by calling
> > > > > drm_atomic_get_crtc_state(),
> > > > > * drm_atomic_get_plane_state(), drm_atomic_get_connector_state(),
> > > > > or for
> > > > > * private state structures, drm_atomic_get_private_obj_state().
> > > > > + *
> > > > > + * NOTE: While this structure looks to be global and affecting the
> > > > > whole DRM
> > > > > + * device, it only contains the objects affected by the atomic
> > > > > commit.
> > > >
> > > > This new phrasing is much more clear to me than the old one.
> > >
> > > Great
> > >
> > > > > + * Unaffected objects will not be part of that update, unless they
> > > > > have been
> > > > > + * explicitly added by either the framework or the driver.
> > > >
> > > > If the framework or a driver adds an object, then it's no longer
> > > > unaffected, is it?
> > >
> > > I guess what I meant to say is that it's affected as a side effect that
> > > the userspace cannot anticipate.
> > >
> > > The typical example being that changing a property on a connector would
> > > need to pull the CRTC into the update to disable / enable the CRTC,
> > > encoder and connector.
> >
> > Right, that's the easy case. This can even be documented and therefore
> > become expected by userspace. The associations between CRTC and
> > connector are published, e.g. the current routing.
> >
> > What I was thinking of was much more hidden:
> >
> > Userspace explicitly programs CRTC A and the connector connected to it.
> > None of the mentioned KMS objects in that atomic commit refer to CRTC B
> > in any way, not in old nor in new device state. Still, the driver
> > decides to pull CRTC B in, because it needs to adjust something there
> > (ISTR hearing "watermarks" in some conversation) in order to
> > accommodate changes in CRTC A.
> >
> > So there are two categories of pulling in extra KMS objects: knowable
> > and unknowable. Or expected and unexpected.
> >
> > If userspace changes things on a connector connected to CRTC A, you can
> > expect to pull in CRTC A. That's knowable. If the driver unexpectedly
> > also pulls in CRTC B while userspace made absolutely no explicit nor
> > implicit reference to it, that's unknowable.
>
> > The unknowable/unexpected additions are very hardware and driver
> > specific and not reliably determinable from an atomic commit UAPI
> > structure.
>
> So I had a quick look at all the drivers we have in-tree, and it looks
> to be either a plane or a connector pulling its CRTC in. I guess they
> would all qualify as knowable.
Yes.
> For unknowable, yeah, it's kind of bad, but at the same time you have to
> deal with the hardware you have. Like, for vc4 for example, there's a
> single controller before the CRTCs that deals with the blending, scaling
> and all the other stuff. That controller has a limited number of FIFOs
> and muxes to output the result of the blending to the right CRTC.
>
> So if you commit something on one CRTC, you might very well wait for
> another one to complete because some hidden state (to userspace) is
> shared between the two and you just can't run them
Re: [PATCH 4/5] drm/atomic: Make the drm_atomic_state documentation less ambiguous
On Fri, Dec 08, 2023 at 10:08:28AM +0200, Pekka Paalanen wrote:
> On Thu, 7 Dec 2023 15:27:33 +0100
> Maxime Ripard wrote:
>
> > On Tue, Dec 05, 2023 at 10:51:06AM +0200, Pekka Paalanen wrote:
> > > On Mon, 4 Dec 2023 13:17:06 +0100
> > > Maxime Ripard wrote:
> > >
> > > > The current documentation of drm_atomic_state says that it's the "global
> > > > state object". This is confusing since, while it does contain all the
> > > > objects affected by an update and their respective states, if an object
> > > > isn't affected by this update it won't be part of it.
> > > >
> > > > Thus, it's not truly a "global state", unlike object state structures
> > > > that do contain the entire state of a given object.
> > > >
> > > > Signed-off-by: Maxime Ripard
> > > > ---
> > > > include/drm/drm_atomic.h | 10 +-
> > > > 1 file changed, 9 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> > > > index 914574b58ae7..81ad7369b90d 100644
> > > > --- a/include/drm/drm_atomic.h
> > > > +++ b/include/drm/drm_atomic.h
> > > > @@ -346,11 +346,19 @@ struct __drm_private_objs_state {
> > > > };
> > > >
> > > > /**
> > > > - * struct drm_atomic_state - the global state object for atomic updates
> > > > + * struct drm_atomic_state - Atomic Update structure
> > > > + *
> > > > + * This structure is the kernel counterpart of @drm_mode_atomic and
> > > > contains
> > > > + * all the objects affected by an atomic modeset update and their
> > > > states.
> > >
> > > Drop "modeset"? An update can be without a modeset.
> >
> > Yeah, good point
> >
> > > > *
> > > > * States are added to an atomic update by calling
> > > > drm_atomic_get_crtc_state(),
> > > > * drm_atomic_get_plane_state(), drm_atomic_get_connector_state(), or
> > > > for
> > > > * private state structures, drm_atomic_get_private_obj_state().
> > > > + *
> > > > + * NOTE: While this structure looks to be global and affecting the
> > > > whole DRM
> > > > + * device, it only contains the objects affected by the atomic commit.
> > > >
> > >
> > > This new phrasing is much more clear to me than the old one.
> >
> > Great
> >
> > > > + * Unaffected objects will not be part of that update, unless they
> > > > have been
> > > > + * explicitly added by either the framework or the driver.
> > >
> > > If the framework or a driver adds an object, then it's no longer
> > > unaffected, is it?
> >
> > I guess what I meant to say is that it's affected as a side effect that
> > the userspace cannot anticipate.
> >
> > The typical example being that changing a property on a connector would
> > need to pull the CRTC into the update to disable / enable the CRTC,
> > encoder and connector.
>
> Right, that's the easy case. This can even be documented and therefore
> become expected by userspace. The associations between CRTC and
> connector are published, e.g. the current routing.
>
> What I was thinking of was much more hidden:
>
> Userspace explicitly programs CRTC A and the connector connected to it.
> None of the mentioned KMS objects in that atomic commit refer to CRTC B
> in any way, not in old nor in new device state. Still, the driver
> decides to pull CRTC B in, because it needs to adjust something there
> (ISTR hearing "watermarks" in some conversation) in order to
> accommodate changes in CRTC A.
>
> So there are two categories of pulling in extra KMS objects: knowable
> and unknowable. Or expected and unexpected.
>
> If userspace changes things on a connector connected to CRTC A, you can
> expect to pull in CRTC A. That's knowable. If the driver unexpectedly
> also pulls in CRTC B while userspace made absolutely no explicit nor
> implicit reference to it, that's unknowable.
> The unknowable/unexpected additions are very hardware and driver
> specific and not reliably determinable from an atomic commit UAPI
> structure.
So I had a quick look at all the drivers we have in-tree, and it looks
to be either a plane or a connector pulling its CRTC in. I guess they
would all qualify as knowable.
For unknowable, yeah, it's kind of bad, but at the same time you have to
deal with the hardware you have. Like, for vc4 for example, there's a
single controller before the CRTCs that deals with the blending, scaling
and all the other stuff. That controller has a limited number of FIFOs
and muxes to output the result of the blending to the right CRTC.
So if you commit something on one CRTC, you might very well wait for
another one to complete because some hidden state (to userspace) is
shared between the two and you just can't run them in parallel.
So yeah... We should strive to make it as transparent to userspace as
possible, but I also don't think we can express all the variations we
support.
> > As far as userspace is concerned, only the connector will be affected,
> > and only the connector will initially be part of the drm_atomic_state.
> >
> > But then some
Re: [PATCH 4/5] drm/atomic: Make the drm_atomic_state documentation less ambiguous
On Thu, 7 Dec 2023 15:27:33 +0100
Maxime Ripard wrote:
> On Tue, Dec 05, 2023 at 10:51:06AM +0200, Pekka Paalanen wrote:
> > On Mon, 4 Dec 2023 13:17:06 +0100
> > Maxime Ripard wrote:
> >
> > > The current documentation of drm_atomic_state says that it's the "global
> > > state object". This is confusing since, while it does contain all the
> > > objects affected by an update and their respective states, if an object
> > > isn't affected by this update it won't be part of it.
> > >
> > > Thus, it's not truly a "global state", unlike object state structures
> > > that do contain the entire state of a given object.
> > >
> > > Signed-off-by: Maxime Ripard
> > > ---
> > > include/drm/drm_atomic.h | 10 +-
> > > 1 file changed, 9 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> > > index 914574b58ae7..81ad7369b90d 100644
> > > --- a/include/drm/drm_atomic.h
> > > +++ b/include/drm/drm_atomic.h
> > > @@ -346,11 +346,19 @@ struct __drm_private_objs_state {
> > > };
> > >
> > > /**
> > > - * struct drm_atomic_state - the global state object for atomic updates
> > > + * struct drm_atomic_state - Atomic Update structure
> > > + *
> > > + * This structure is the kernel counterpart of @drm_mode_atomic and
> > > contains
> > > + * all the objects affected by an atomic modeset update and their
> > > states.
> >
> > Drop "modeset"? An update can be without a modeset.
>
> Yeah, good point
>
> > > *
> > > * States are added to an atomic update by calling
> > > drm_atomic_get_crtc_state(),
> > > * drm_atomic_get_plane_state(), drm_atomic_get_connector_state(), or for
> > > * private state structures, drm_atomic_get_private_obj_state().
> > > + *
> > > + * NOTE: While this structure looks to be global and affecting the whole
> > > DRM
> > > + * device, it only contains the objects affected by the atomic commit.
> >
> > This new phrasing is much more clear to me than the old one.
>
> Great
>
> > > + * Unaffected objects will not be part of that update, unless they have
> > > been
> > > + * explicitly added by either the framework or the driver.
> >
> > If the framework or a driver adds an object, then it's no longer
> > unaffected, is it?
>
> I guess what I meant to say is that it's affected as a side effect that
> the userspace cannot anticipate.
>
> The typical example being that changing a property on a connector would
> need to pull the CRTC into the update to disable / enable the CRTC,
> encoder and connector.
Right, that's the easy case. This can even be documented and therefore
become expected by userspace. The associations between CRTC and
connector are published, e.g. the current routing.
What I was thinking of was much more hidden:
Userspace explicitly programs CRTC A and the connector connected to it.
None of the mentioned KMS objects in that atomic commit refer to CRTC B
in any way, not in old nor in new device state. Still, the driver
decides to pull CRTC B in, because it needs to adjust something there
(ISTR hearing "watermarks" in some conversation) in order to
accommodate changes in CRTC A.
So there are two categories of pulling in extra KMS objects: knowable
and unknowable. Or expected and unexpected.
If userspace changes things on a connector connected to CRTC A, you can
expect to pull in CRTC A. That's knowable. If the driver unexpectedly
also pulls in CRTC B while userspace made absolutely no explicit nor
implicit reference to it, that's unknowable.
The unknowable/unexpected additions are very hardware and driver
specific and not reliably determinable from an atomic commit UAPI
structure.
> As far as userspace is concerned, only the connector will be affected,
> and only the connector will initially be part of the drm_atomic_state.
>
> But then some part of the atomic_check logic will pull the CRTC into the
> update.
Is this a rule that happens always? If so, it can be documented to make
it expected.
> It's still invisible to userspace, so I guess
> "unaffected-but-turns-out-to-be-affected" would be the right term :)
>
> Would something like:
>
> Unaffected objects will not be part of the initial update, but might be
> added explicitly by either the framework or the driver during
> atomic_check.
>
> be better?
I'm not comfortable with the use of "unaffected" here. I'd be more in
the direction of: More objects can be affected than explicitly
mentioned.
Thanks,
pq
> > Should there be some discussion how this struct starts with only what
> > userspace mentioned, and more affected objects may be added by the
> > framework or a driver? And adding more objects can surprise the
> > userspace and cause even failures (e.g. random, hard-to-diagnose EBUSY
> > errors from atomic commit when a driver added a CRTC that was not
> > supposed to be affected)? Even unexpected failures on *future* atomic
> > commits, as in the CRTC example.
> >
> > Was there actually a rule of when the
Re: [PATCH 4/5] drm/atomic: Make the drm_atomic_state documentation less ambiguous
On Mon, Dec 04, 2023 at 01:17:06PM +0100, Maxime Ripard wrote:
> The current documentation of drm_atomic_state says that it's the "global
> state object". This is confusing since, while it does contain all the
> objects affected by an update and their respective states, if an object
> isn't affected by this update it won't be part of it.
>
> Thus, it's not truly a "global state", unlike object state structures
> that do contain the entire state of a given object.
>
> Signed-off-by: Maxime Ripard
So this is probably the biggest naming fumble I've committed, because this
is the drm_atomic_commit structure: It's not just a state structure, but
it represents the transition from a set of old to new states. Which is
also why we have both old and new state pointers in it.
> ---
> include/drm/drm_atomic.h | 10 +-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> index 914574b58ae7..81ad7369b90d 100644
> --- a/include/drm/drm_atomic.h
> +++ b/include/drm/drm_atomic.h
> @@ -346,11 +346,19 @@ struct __drm_private_objs_state {
> };
>
> /**
> - * struct drm_atomic_state - the global state object for atomic updates
> + * struct drm_atomic_state - Atomic Update structure
I think we're using "commit" more often than "update"
> + *
> + * This structure is the kernel counterpart of @drm_mode_atomic and contains
> + * all the objects affected by an atomic modeset update and their states.
My suggestion:
This structure is the kernel counterpart of @drm_mode_atomic and
represents an atomic commit that transitions from an old to a new display
state. It contains all the objects affected by an atomic commits and both
the new state structures and pointers to the old state structures for
these.
> *
> * States are added to an atomic update by calling
> drm_atomic_get_crtc_state(),
> * drm_atomic_get_plane_state(), drm_atomic_get_connector_state(), or for
> * private state structures, drm_atomic_get_private_obj_state().
> + *
> + * NOTE: While this structure looks to be global and affecting the whole DRM
> + * device, it only contains the objects affected by the atomic commit.
> + * Unaffected objects will not be part of that update, unless they have been
> + * explicitly added by either the framework or the driver.
Since you remove the global in the header summary I wouldn't reintroduce
it here. Seems to just add to the confusion again instead of clarifying.
If you want maybe clarify that an atomic commit does not need to contain
all the objects of a _device, or something like that.
With the comments suitably addressed:
Reviewed-by: Daniel Vetter
> */
> struct drm_atomic_state {
> /**
> --
> 2.43.0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
Re: [PATCH 4/5] drm/atomic: Make the drm_atomic_state documentation less ambiguous
On Tue, Dec 05, 2023 at 10:51:06AM +0200, Pekka Paalanen wrote:
> On Mon, 4 Dec 2023 13:17:06 +0100
> Maxime Ripard wrote:
>
> > The current documentation of drm_atomic_state says that it's the "global
> > state object". This is confusing since, while it does contain all the
> > objects affected by an update and their respective states, if an object
> > isn't affected by this update it won't be part of it.
> >
> > Thus, it's not truly a "global state", unlike object state structures
> > that do contain the entire state of a given object.
> >
> > Signed-off-by: Maxime Ripard
> > ---
> > include/drm/drm_atomic.h | 10 +-
> > 1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> > index 914574b58ae7..81ad7369b90d 100644
> > --- a/include/drm/drm_atomic.h
> > +++ b/include/drm/drm_atomic.h
> > @@ -346,11 +346,19 @@ struct __drm_private_objs_state {
> > };
> >
> > /**
> > - * struct drm_atomic_state - the global state object for atomic updates
> > + * struct drm_atomic_state - Atomic Update structure
> > + *
> > + * This structure is the kernel counterpart of @drm_mode_atomic and
> > contains
> > + * all the objects affected by an atomic modeset update and their states.
>
> Drop "modeset"? An update can be without a modeset.
Yeah, good point
> > *
> > * States are added to an atomic update by calling
> > drm_atomic_get_crtc_state(),
> > * drm_atomic_get_plane_state(), drm_atomic_get_connector_state(), or for
> > * private state structures, drm_atomic_get_private_obj_state().
> > + *
> > + * NOTE: While this structure looks to be global and affecting the whole
> > DRM
> > + * device, it only contains the objects affected by the atomic commit.
>
> This new phrasing is much more clear to me than the old one.
Great
> > + * Unaffected objects will not be part of that update, unless they have
> > been
> > + * explicitly added by either the framework or the driver.
>
> If the framework or a driver adds an object, then it's no longer
> unaffected, is it?
I guess what I meant to say is that it's affected as a side effect that
the userspace cannot anticipate.
The typical example being that changing a property on a connector would
need to pull the CRTC into the update to disable / enable the CRTC,
encoder and connector.
As far as userspace is concerned, only the connector will be affected,
and only the connector will initially be part of the drm_atomic_state.
But then some part of the atomic_check logic will pull the CRTC into the
update.
It's still invisible to userspace, so I guess
"unaffected-but-turns-out-to-be-affected" would be the right term :)
Would something like:
Unaffected objects will not be part of the initial update, but might be
added explicitly by either the framework or the driver during
atomic_check.
be better?
> Should there be some discussion how this struct starts with only what
> userspace mentioned, and more affected objects may be added by the
> framework or a driver? And adding more objects can surprise the
> userspace and cause even failures (e.g. random, hard-to-diagnose EBUSY
> errors from atomic commit when a driver added a CRTC that was not
> supposed to be affected)? Even unexpected failures on *future* atomic
> commits, as in the CRTC example.
>
> Was there actually a rule of when the kernel can add unmentioned
> objects, like needing ALLOW_MODESET from userspace?
Sima (iirc?) recently made that explicit, yeah, but there's plenty of
commits that need at the very least the encoder and connector to be
disabled and enabled again to handle them.
Maxime
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Re: [PATCH 4/5] drm/atomic: Make the drm_atomic_state documentation less ambiguous
On Tue, Dec 05, 2023 at 11:15:29AM +0200, Pekka Paalanen wrote: > On Tue, 5 Dec 2023 10:51:06 +0200 > Pekka Paalanen wrote: > > > On Mon, 4 Dec 2023 13:17:06 +0100 > > Maxime Ripard wrote: > > > > > The current documentation of drm_atomic_state says that it's the "global > > > state object". This is confusing since, while it does contain all the > > > objects affected by an update and their respective states, if an object > > > isn't affected by this update it won't be part of it. > > > > > > Thus, it's not truly a "global state", unlike object state structures > > > that do contain the entire state of a given object. > > > > > > Signed-off-by: Maxime Ripard > > could you figure out how your email got the linux.ie address for Dave > Airlie? > > I got a bounce from skynet.ie when replying to all. Maybe there is a > leftover email address for Dave still somewhere? Yep. In my mutt aliases file :) It's fixed now, thanks Maxime signature.asc Description: PGP signature
Re: [PATCH 4/5] drm/atomic: Make the drm_atomic_state documentation less ambiguous
On Tue, 5 Dec 2023 10:51:06 +0200 Pekka Paalanen wrote: > On Mon, 4 Dec 2023 13:17:06 +0100 > Maxime Ripard wrote: > > > The current documentation of drm_atomic_state says that it's the "global > > state object". This is confusing since, while it does contain all the > > objects affected by an update and their respective states, if an object > > isn't affected by this update it won't be part of it. > > > > Thus, it's not truly a "global state", unlike object state structures > > that do contain the entire state of a given object. > > > > Signed-off-by: Maxime Ripard Hi Maxime, could you figure out how your email got the linux.ie address for Dave Airlie? I got a bounce from skynet.ie when replying to all. Maybe there is a leftover email address for Dave still somewhere? Thanks, pq pgpGC8eRN_2is.pgp Description: OpenPGP digital signature
Re: [PATCH 4/5] drm/atomic: Make the drm_atomic_state documentation less ambiguous
On Mon, 4 Dec 2023 13:17:06 +0100
Maxime Ripard wrote:
> The current documentation of drm_atomic_state says that it's the "global
> state object". This is confusing since, while it does contain all the
> objects affected by an update and their respective states, if an object
> isn't affected by this update it won't be part of it.
>
> Thus, it's not truly a "global state", unlike object state structures
> that do contain the entire state of a given object.
>
> Signed-off-by: Maxime Ripard
> ---
> include/drm/drm_atomic.h | 10 +-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> index 914574b58ae7..81ad7369b90d 100644
> --- a/include/drm/drm_atomic.h
> +++ b/include/drm/drm_atomic.h
> @@ -346,11 +346,19 @@ struct __drm_private_objs_state {
> };
>
> /**
> - * struct drm_atomic_state - the global state object for atomic updates
> + * struct drm_atomic_state - Atomic Update structure
> + *
> + * This structure is the kernel counterpart of @drm_mode_atomic and contains
> + * all the objects affected by an atomic modeset update and their states.
Drop "modeset"? An update can be without a modeset.
> *
> * States are added to an atomic update by calling
> drm_atomic_get_crtc_state(),
> * drm_atomic_get_plane_state(), drm_atomic_get_connector_state(), or for
> * private state structures, drm_atomic_get_private_obj_state().
> + *
> + * NOTE: While this structure looks to be global and affecting the whole DRM
> + * device, it only contains the objects affected by the atomic commit.
This new phrasing is much more clear to me than the old one.
> + * Unaffected objects will not be part of that update, unless they have been
> + * explicitly added by either the framework or the driver.
If the framework or a driver adds an object, then it's no longer
unaffected, is it?
Should there be some discussion how this struct starts with only what
userspace mentioned, and more affected objects may be added by the
framework or a driver? And adding more objects can surprise the
userspace and cause even failures (e.g. random, hard-to-diagnose EBUSY
errors from atomic commit when a driver added a CRTC that was not
supposed to be affected)? Even unexpected failures on *future* atomic
commits, as in the CRTC example.
Was there actually a rule of when the kernel can add unmentioned
objects, like needing ALLOW_MODESET from userspace?
It's fine to leave those details for later if you want.
> */
> struct drm_atomic_state {
> /**
Thanks,
pq
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