Re: [PATCH v3 12/20] drm/crtc: Add new atomic_create_state callback

[Maxime Ripard <mripard@kernel.org>]

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Hi,

On Mon, May 04, 2026 at 08:28:58PM +0300, Laurent Pinchart wrote:
> On Fri, Apr 24, 2026 at 12:18:52PM +0200, Maxime Ripard wrote:
> > Commit 47b5ac7daa46 ("drm/atomic: Add new atomic_create_state callback
> > to drm_private_obj") introduced a new pattern for allocating drm object
> > states.
> > 
> > Instead of relying on the reset() callback, it created a new
> > atomic_create_state hook. This is helpful because reset is a bit
> > overloaded: it's used to create the initial software state, reset it,
> > but also reset the hardware.
> > 
> > It can also be used either at probe time, to create the initial state
> > and possibly reset the hardware to an expected default, but also during
> > suspend/resume.
> > 
> > Both these cases come with different expectations too: during the
> > initialization, we want to initialize all states, but during
> > suspend/resume, drm_private_states for example are expected to be kept
> > around.
> > 
> > reset() also isn't fallible, which makes it harder to handle
> > initialization errors properly. This is only really relevant for some
> > drivers though, since all the helpers for reset only create a new
> > state, and don't touch the hardware at all.
> > 
> > It was thus decided to create a new hook that would allocate and
> > initialize a pristine state without any side effect:
> > atomic_create_state to untangle a bit some of it, and to separate the
> > initialization with the actual reset one might need during a
> > suspend/resume.
> > 
> > Continue the transition to the new pattern with CRTCs.
> > 
> > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> > Signed-off-by: Maxime Ripard <mripard@kernel.org>
> > ---
> >  drivers/gpu/drm/drm_atomic_state_helper.c | 47 +++++++++++++++++++++++++++++++
> >  drivers/gpu/drm/drm_mode_config.c         | 21 +++++++++++++-
> >  include/drm/drm_atomic_state_helper.h     |  4 +++
> >  include/drm/drm_crtc.h                    | 16 +++++++++++
> >  4 files changed, 87 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
> > index 9cd8550cabb7..b7da134c8c50 100644
> > --- a/drivers/gpu/drm/drm_atomic_state_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
> > @@ -103,10 +103,32 @@ __drm_atomic_helper_crtc_reset(struct drm_crtc *crtc,
> >  
> >  	crtc->state = crtc_state;
> >  }
> >  EXPORT_SYMBOL(__drm_atomic_helper_crtc_reset);
> >  
> > +/**
> > + * __drm_atomic_helper_crtc_create_state - initializes crtc state
> 
> "Initialize a CRTC state"

Good catch, thanks.

> The name of the function is misleading ("*_create_*" while you state it
> performs initialization).
>
> > + * @crtc: crtc object
> > + * @state: new state to initialize
> > + *
> > + * Initializes the newly allocated @state, usually required when
> > + * initializing the drivers.
> > + *
> > + * @state is assumed to be zeroed.
> > + *
> > + * This is useful for drivers that subclass @drm_crtc_state.
> > + */
> > +void __drm_atomic_helper_crtc_create_state(struct drm_crtc *crtc,
> > +					   struct drm_crtc_state *state)
> > +{
> > +	__drm_atomic_helper_crtc_state_init(state, crtc);
> > +
> > +	if (drm_dev_has_vblank(crtc->dev))
> > +		drm_crtc_vblank_reset(crtc);
> 
> This is confusing to me (at least before reading the rest of the
> series), and itn't mentioned in the function documentation or in the
> commit message.
>
> Furthermore, __drm_atomic_helper_crtc_create_state() is later used in
> tidss_crtc_create_state(), which is the
> drm_crtc_funcs.atomic_create_state() implementation of the tidss driver.
> The atomic_create_state documentation states that "This callback must
> have no side effect", and drm_crtc_vblank_reset() has side effects.

That's a good point. I've dropped that function entirely and moved the
drm_crtc_vblank_reset() call in drm_mode_config_crtc_create_state().

Maxime

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