[PATCH v2 1/4] drm/panel: Add new helpers for refcounted panel allocatons

[Maxime Ripard]

On Thu, Mar 27, 2025 at 11:33:15AM -0400, Anusha Srivatsa wrote:
> On Thu, Mar 27, 2025 at 11:58 AM Maxime Ripard <mripard at kernel.org> wrote:
> 
> > On Thu, Mar 27, 2025 at 10:55:39AM -0400, Anusha Srivatsa wrote:
> > > Introduce reference counted allocations for panels to avoid
> > > use-after-free. The patch adds the macro devm_drm_bridge_alloc()
> > > to allocate a new refcounted panel. Followed the documentation for
> > > drmm_encoder_alloc() and devm_drm_dev_alloc and other similar
> > > implementations for this purpose.
> > >
> > > v2: Better documentation for connector_type field - follow drm_panel_init
> > > documentation. (Luca)
> > > - Clarify the refcount initialisation in comments.(Maxime)
> > > - Correct the documentation of the return type (Maxime)
> > >
> > > Signed-off-by: Anusha Srivatsa <asrivats at redhat.com>
> > > ---
> > >  drivers/gpu/drm/drm_panel.c | 25 +++++++++++++++++++++++++
> > >  include/drm/drm_panel.h     | 23 +++++++++++++++++++++++
> > >  2 files changed, 48 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> > > index
> > c627e42a7ce70459f50eb5095fffc806ca45dabf..bdeab5710ee324dc1742fbc77582250960556308
> > 100644
> > > --- a/drivers/gpu/drm/drm_panel.c
> > > +++ b/drivers/gpu/drm/drm_panel.c
> > > @@ -355,6 +355,31 @@ struct drm_panel *of_drm_find_panel(const struct
> > device_node *np)
> > >  }
> > >  EXPORT_SYMBOL(of_drm_find_panel);
> > >
> > > +void *__devm_drm_panel_alloc(struct device *dev, size_t size, size_t
> > offset,
> > > +                          const struct drm_panel_funcs *funcs,
> > > +                          int connector_type)
> > > +{
> > > +     void *container;
> > > +     struct drm_panel *panel;
> > > +
> > > +     if (!funcs) {
> > > +             dev_warn(dev, "Missing funcs pointer\n");
> > > +             return ERR_PTR(-EINVAL);
> > > +     }
> > > +
> > > +     container = devm_kzalloc(dev, size, GFP_KERNEL);
> > > +     if (!container)
> > > +             return ERR_PTR(-ENOMEM);
> > > +
> > > +     panel = container + offset;
> > > +     panel->funcs = funcs;
> > > +
> > > +     drm_panel_init(panel, dev, funcs, connector_type);
> > > +
> > > +     return container;
> > > +}
> > > +EXPORT_SYMBOL(__devm_drm_panel_alloc);
> > > +
> > >  /**
> > >   * of_drm_get_panel_orientation - look up the orientation of the panel
> > through
> > >   * the "rotation" binding from a device tree node
> > > diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> > > index
> > a9c042c8dea1a82ef979c7a68204e0b55483fc28..53251c6b11d78149ede3dad41ffa6a88f3c3c58b
> > 100644
> > > --- a/include/drm/drm_panel.h
> > > +++ b/include/drm/drm_panel.h
> > > @@ -28,6 +28,7 @@
> > >  #include <linux/errno.h>
> > >  #include <linux/list.h>
> > >  #include <linux/mutex.h>
> > > +#include <linux/kref.h>
> > >
> > >  struct backlight_device;
> > >  struct dentry;
> > > @@ -268,6 +269,28 @@ struct drm_panel {
> > >       bool enabled;
> > >  };
> > >
> > > +void *__devm_drm_panel_alloc(struct device *dev, size_t size, size_t
> > offset,
> > > +                          const struct drm_panel_funcs *funcs,
> > > +                          int connector_type);
> > > +
> > > +/**
> > > + * devm_drm_panel_alloc - Allocate and initialize an refcounted panel
> > > + * @dev: struct device of the panel device
> > > + * @type: the type of the struct which contains struct &drm_panel
> > > + * @member: the name of the &drm_panel within @type
> > > + * @funcs: callbacks for this panel
> > > + * @connector_type: the connector type (DRM_MODE_CONNECTOR_*)
> > corresponding to
> > > + * the panel interface
> > > + * Returns:
> > > + * Pointer to container structure embedding the panel, ERR_PTR on
> > failure.
> > > + * The reference count is initialised to 1 and is automatically  given
> > back
> > > + * by devm action.
> >
> > Sorry, I noticed after the facts, but this can't be in the Returns
> > section, it needs to be in the main one.
>
> Maxime, Not really following you. Are you suggesting this explanation
> needs to be in the helper documentation instead of in returns?

This is a general documentation thing, so it needs to be in the main
documentation section, thus between the argumnts and returned values
one.

Maxime
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