Re: [PATCH v2 1/8] drm: Add crtc/encoder/bridge->mode_valid() callbacks

[Laurent Pinchart]

Hi Daniel,

On Wednesday 10 May 2017 10:03:37 Daniel Vetter wrote:
> On Tue, May 09, 2017 at 06:00:08PM +0100, Jose Abreu wrote:
> > This adds a new callback to crtc, encoder and bridge helper functions
> > called mode_valid(). This callback shall be implemented if the
> > corresponding component has some sort of restriction in the modes
> > that can be displayed. A NULL callback implicates that the component
> > can display all the modes.
> > 
> > We also change the description of connector->mode_valid() callback
> > so that it matches the existing behaviour: It is never called in
> > atomic check phase.
> > 
> > Only the callbacks were implemented to simplify review process,
> > following patches will make use of them.
> > 
> > Signed-off-by: Jose Abreu <joabreu@xxxxxxxxxxxx>
> > Cc: Carlos Palminha <palminha@xxxxxxxxxxxx>
> > Cc: Alexey Brodkin <abrodkin@xxxxxxxxxxxx>
> > Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > Cc: Dave Airlie <airlied@xxxxxxxx>
> > Cc: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> > Cc: Archit Taneja <architt@xxxxxxxxxxxxxx>
> > ---
> > 
> > Changes v1->v2:
> > 	- Change description of connector->mode_valid() (Daniel)
> > 	
> >  include/drm/drm_bridge.h                 | 20 ++++++++++++++
> >  include/drm/drm_modeset_helper_vtables.h | 45 +++++++++++++++++++++++++++
> >  2 files changed, 65 insertions(+)
> > 
> > diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> > index fdd82fc..00c6c36 100644
> > --- a/include/drm/drm_bridge.h
> > +++ b/include/drm/drm_bridge.h
> > @@ -59,6 +59,26 @@ struct drm_bridge_funcs {
> >  	void (*detach)(struct drm_bridge *bridge);
> >  	
> >  	/**
> > +	 * @mode_valid:
> > +	 *
> > +	 * This callback is used to check if a specific mode is valid in this
> > +	 * bridge. This should be implemented if the bridge has some sort of
> > +	 * restriction in the modes it can display. For example, a given 
bridge
> > +	 * may be responsible to set a clock value. If the clock can not
> > +	 * produce all the values for the available modes then this callback
> > +	 * can be used to restrict the number of modes to only the ones that
> > +	 * can be displayed.
> > +	 *
> > +	 * This is called at mode probe and at atomic check phase.
> > +	 *
> > +	 * RETURNS:
> > +	 *
> > +	 * drm_mode_status Enum
> > +	 */
> > +	enum drm_mode_status (*mode_valid)(struct drm_bridge *crtc,
> > +					   const struct drm_display_mode 
*mode);
> > +
> > +	/**
> >  	 * @mode_fixup:
> >  	 *
> >  	 * This callback is used to validate and adjust a mode. The paramater
> > diff --git a/include/drm/drm_modeset_helper_vtables.h
> > b/include/drm/drm_modeset_helper_vtables.h index c01c328..eec2c70 100644
> > --- a/include/drm/drm_modeset_helper_vtables.h
> > +++ b/include/drm/drm_modeset_helper_vtables.h
> > @@ -106,6 +106,26 @@ struct drm_crtc_helper_funcs {
> >  	void (*commit)(struct drm_crtc *crtc);
> >  	
> >  	/**
> > +	 * @mode_valid:
> > +	 *
> > +	 * This callback is used to check if a specific mode is valid in this
> > +	 * crtc. This should be implemented if the crtc has some sort of
> > +	 * restriction in the modes it can display. For example, a given crtc
> > +	 * may be responsible to set a clock value. If the clock can not
> > +	 * produce all the values for the available modes then this callback
> > +	 * can be used to restrict the number of modes to only the ones that
> > +	 * can be displayed.
> > +	 *
> > +	 * This is called at mode probe and at atomic check phase.
> > +	 *
> > +	 * RETURNS:
> > +	 *
> > +	 * drm_mode_status Enum
> > +	 */
> > +	enum drm_mode_status (*mode_valid)(struct drm_crtc *crtc,
> > +					   const struct drm_display_mode 
*mode);
> > +
> > +	/**
> >  	 * @mode_fixup:
> >  	 *
> >  	 * This callback is used to validate a mode. The parameter mode is the
> > @@ -457,6 +477,26 @@ struct drm_encoder_helper_funcs {
> >  	void (*dpms)(struct drm_encoder *encoder, int mode);
> >  	
> >  	/**
> > +	 * @mode_valid:
> > +	 *
> > +	 * This callback is used to check if a specific mode is valid in this
> > +	 * encoder. This should be implemented if the encoder has some sort
> > +	 * of restriction in the modes it can display. For example, a given
> > +	 * encoder may be responsible to set a clock value. If the clock can
> > +	 * not produce all the values for the available modes then this 
callback
> > +	 * can be used to restrict the number of modes to only the ones that
> > +	 * can be displayed.
> > +	 *
> > +	 * This is called at mode probe and at atomic check phase.
> > +	 *
> > +	 * RETURNS:
> > +	 *
> > +	 * drm_mode_status Enum
> > +	 */
> > +	enum drm_mode_status (*mode_valid)(struct drm_encoder *crtc,
> > +					   const struct drm_display_mode 
*mode);
> > +
> > +	/**
> >  	 * @mode_fixup:
> >  	 *
> >  	 * This callback is used to validate and adjust a mode. The parameter
> > @@ -795,6 +835,11 @@ struct drm_connector_helper_funcs {
> >  	 * (which is usually derived from the EDID data block from the sink).
> >  	 * See e.g. drm_helper_probe_single_connector_modes().
> >  	 *
> > +	 * This callback is never called in atomic check phase so that 
userspace
> > +	 * can override kernel sink checks in case of broken EDID with wrong
> > +	 * limits from the sink. You can use the remaining mode_valid()
> > +	 * callbacks to validate the mode against your video path.
> > +	 *
> >  	 * NOTE:
> >  	 *
> >  	 * This only filters the mode list supplied to userspace in the
> 
> Kerneldoc review seems to still be missing. One case that needs to be
> updated is this note here. But there's a pile of other places where we
> reference one of the mode_valid or mode_fixup functions, and they should
> all be updated.
> 
> Also, it'd be good to explain what to put into mode_valid and what to put
> into mode_fixup, for objects which have both. I can help with this, but I
> think it'd be good if you make a first round, since that might catch some
> interactions we've missed.

I was going to mention that. Interactions between mode_valid and mode_fixup 
are not defined clearly. Additionally, even though it might be a bit out of 
scope for this patch series, I think we should also define what mode_fixup is 
allowed to fix and what it should reject straight away.

Thinking about it, do we really need two separate operations ? As I understand 
it, mode_fixup is mostly (only ? - this is where we need documentation) used 
to fixup the pixel clock frequency as clock generators usually have 
limitations in their dividers. We assume that the sync won't care too much, 
and happily feed it with a mode that is slightly different from what userspace 
requested. Given that mode_valid should accepts mode for which the exact pixel 
clock frequency can't bee achieved, and that the atomic commit will fixup that 
frequency anyway, can't we apply the same processing to modes enumerated by 
the connector, and merge the mode_valid and mode_fixup operations ?

-- 
Regards,

Laurent Pinchart