[PATCH] drm/simple_kms_helper: add drmm_simple_encoder_init()

[Daniel Vetter]

On Thu, Jul 23, 2020 at 9:36 AM Thomas Zimmermann <tzimmermann at suse.de> wrote:
>
> Hi
>
> I have meanwhile seen your imx patchset where this would be useful.
>
> I still think you should try to pre-allocated all encoders up to a
> limit, so that an extra drmm_kzalloc() is not required. But see my
> comments below.

Uh preallocation is horribly, because you need to first preallocate
all encoders, then call drmm_mode_config_init, and only then can you
call  drm_encoder_init. That's terrible flow, and I'm aware of the
problem. That's why we need new set of drmm_ helpers to do all the
steps for kms static object setup, if we actually want to improve
things.
-Daniel

>
> 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)
>
> It's the reset helper, so drmm_simple_encoder_reset() would be appropriate.
>
> > +{
> > +     struct drm_encoder *encoder = ptr;
> > +
> > +     drm_encoder_cleanup(encoder);
>
> This should first check for (encoder->dev) being true. If drivers
> somehow manage to clean-up the mode config first, we should detect it. I
> know it's a bug, but I wouldn't trust drivers with that.
>
> > +}
> > +
> > +/**
> > + * drmm_simple_encoder_init - Initialize a preallocated encoder with
> > + *                            basic functionality.
> > + * @dev: drm device
> > + * @encoder: the encoder to initialize
> > + * @encoder_type: user visible type of the encoder
> > + *
> > + * Initialises a preallocated encoder that has no further functionality.
>
> 'Initializes'
>
> > + * Settings for possible CRTC and clones are left to their initial values.
> > + * Cleanup is automatically handled through registering drm_encoder_cleanup()
> > + * with drmm_add_action().
> > + *
> > + * The caller of drmm_simple_encoder_init() is responsible for allocating
> > + * the encoder's memory with drmm_kzalloc() to ensure it is automatically
> > + * freed after the encoder has been cleaned up.
> > + *
>
> The idiomatic way of cleaning up an encoder is via mode-config cleanup.
> This interface is an exception for a corner case. So there needs to be a
> paragraph that clearly explains the corner case. Please also discourage
> from using drmm_simple_encoder_init() if drm_simple_encoder_init() would
> work.
>
> Best regards
> Thomas
>
> > + * Returns:
> > + * Zero on success, error code on failure.
> > + */
> > +int drmm_simple_encoder_init(struct drm_device *dev,
> > +                          struct drm_encoder *encoder,
> > +                          int encoder_type)
> > +{
> > +     int ret;
> > +
> > +     ret = drm_encoder_init(dev, encoder, &drm_simple_encoder_funcs_cleanup,
> > +                            encoder_type, NULL);
> > +     if (ret)
> > +             return ret;
> > +
> > +     return drmm_add_action_or_reset(dev, drmm_encoder_cleanup, encoder);
> > +}
> > +EXPORT_SYMBOL(drmm_simple_encoder_init);
> > +
> >  static enum drm_mode_status
> >  drm_simple_kms_crtc_mode_valid(struct drm_crtc *crtc,
> >                              const struct drm_display_mode *mode)
> > diff --git a/include/drm/drm_simple_kms_helper.h b/include/drm/drm_simple_kms_helper.h
> > index a026375464ff..27f0915599c8 100644
> > --- a/include/drm/drm_simple_kms_helper.h
> > +++ b/include/drm/drm_simple_kms_helper.h
> > @@ -185,4 +185,8 @@ int drm_simple_encoder_init(struct drm_device *dev,
> >                           struct drm_encoder *encoder,
> >                           int encoder_type);
> >
> > +int drmm_simple_encoder_init(struct drm_device *dev,
> > +                          struct drm_encoder *encoder,
> > +                          int encoder_type);
> > +
> >  #endif /* __LINUX_DRM_SIMPLE_KMS_HELPER_H */
> >
>
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
>
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch