Re: [PATCH v4 01/19] drm/encoder: make encoder control functions optional

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Dec 09, 2020 at 11:58:44AM +0100, Philipp Zabel wrote:
> Hi Sam,
> 
> On Tue, 2020-12-08 at 19:48 +0100, Sam Ravnborg wrote:
> > Hi Philipp,
> > On Tue, Dec 08, 2020 at 04:54:33PM +0100, Philipp Zabel wrote:
> > > Simple managed encoders do not require the .destroy callback,
> > > make the whole funcs structure optional.
> > > 
> > > Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
> > > Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > ---
> > > New in v4.
> > > ---
> > >  drivers/gpu/drm/drm_encoder.c     | 4 ++--
> > >  drivers/gpu/drm/drm_mode_config.c | 5 +++--
> > >  include/drm/drm_encoder.h         | 2 +-
> > >  3 files changed, 6 insertions(+), 5 deletions(-)
> > > 
> [...]
> > > diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> > > index f1affc1bb679..87e144155456 100644
> > > --- a/drivers/gpu/drm/drm_mode_config.c
> > > +++ b/drivers/gpu/drm/drm_mode_config.c
> [...]
> > > @@ -487,7 +487,8 @@ void drm_mode_config_cleanup(struct drm_device *dev)
> > >  
> > >  	list_for_each_entry_safe(encoder, enct, &dev->mode_config.encoder_list,
> > >  				 head) {
> > > -		encoder->funcs->destroy(encoder);
> > > +		if (encoder->funcs)
> > > +			encoder->funcs->destroy(encoder);
> > 
> > So late_register and early_unregister are both optional.
> > But if encoder->funcs is set then the destroy callback is mandatory.
> 
> For encoders that are kept on the mode_config.encoder_list until
> drm_mode_config_cleanup() is called, the destroy callback is still
> mandatory.
> 
> Encoders allocated with drmm_encoder_alloc() on the other hand should
> have the destroy callback set to NULL, if encoder->funcs is set.
> These encoders are removed from the mode_config.encoder_list by the drmm
> cleanup code, before drm_mode_config_cleanup is called.
> 
> > I am just wondering if this is intended.
> > Reding the documnetation of drm_encoder_funcs thist matches the
> > documentation but anyway..
> >
> > With this comment considered,
> > Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
> 
> Thank you for bringing this up, should we just leave
> drm_mode_config_cleanup() as-is?

Yup, not having a funcs->destroy there is a bug. Maybe should even warn
about the lack of that in the traditional non-drmm_ encoder init function.
-Daniel

> 
> regards
> Philipp
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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