[PATCH] drm/simple_kms_helper: add drmm_simple_encoder_init()

[Philipp Zabel]

Hi Thomas,

thank you for your comment.

On Wed, 2020-07-22 at 16:43 +0200, Thomas Zimmermann wrote:
> Hi
> 
> Am 22.07.20 um 15:25 schrieb Philipp Zabel:
> > Add a drm_simple_encoder_init() variant that registers
> > drm_encoder_cleanup() with drmm_add_action().
> > 
> > Now drivers can store encoders in memory allocated with drmm_kmalloc()
> > after the call to drmm_mode_config_init(), without having to manually
> > make sure that drm_encoder_cleanup() is called before the memory is
> > freed.
> > 
> > Signed-off-by: Philipp Zabel <p.zabel at pengutronix.de>
> > ---
> >  drivers/gpu/drm/drm_simple_kms_helper.c | 42 +++++++++++++++++++++++++
> >  include/drm/drm_simple_kms_helper.h     |  4 +++
> >  2 files changed, 46 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_simple_kms_helper.c b/drivers/gpu/drm/drm_simple_kms_helper.c
> > index 74946690aba4..a243f00cf63d 100644
> > --- a/drivers/gpu/drm/drm_simple_kms_helper.c
> > +++ b/drivers/gpu/drm/drm_simple_kms_helper.c
> > @@ -9,6 +9,7 @@
> >  #include <drm/drm_atomic.h>
> >  #include <drm/drm_atomic_helper.h>
> >  #include <drm/drm_bridge.h>
> > +#include <drm/drm_managed.h>
> >  #include <drm/drm_plane_helper.h>
> >  #include <drm/drm_probe_helper.h>
> >  #include <drm/drm_simple_kms_helper.h>
> > @@ -71,6 +72,47 @@ int drm_simple_encoder_init(struct drm_device *dev,
> >  }
> >  EXPORT_SYMBOL(drm_simple_encoder_init);
> >  
> > +static void drmm_encoder_cleanup(struct drm_device *dev, void *ptr)
> > +{
> > +	struct drm_encoder *encoder = ptr;
> > +
> > +	drm_encoder_cleanup(encoder);
> > +}
> 
> This doesn't work. DRM cleans up the encoder by invoking the destroy
> callback from the encoder functions. This additional helper would
> cleanup the encoder a second time.

Indeed this would require the encoder destroy callback to be NULL.

> You can already embed the encoder in another structure and things should
> work as expected.

If the embedding structure is a component allocated with drmm_kmalloc()
after the call to drmm_mode_config_init(), the structure will already be
freed before the destroy callback is run from
drmm_mode_config_init_release().

regards
Philipp