[RESEND PATCH v11 02/18] drm: bridge: panel: Add devm_drm_of_dsi_get_bridge helper

[Maxime Ripard]

On Thu, Jan 26, 2023 at 08:48:48PM +0530, Jagan Teki wrote:
> On Thu, Jan 26, 2023 at 5:42 PM Maxime Ripard <maxime at cerno.tech> wrote:
> >
> > Hi,
> >
> > On Mon, Jan 23, 2023 at 08:41:56PM +0530, Jagan Teki wrote:
> > > Add devm OF helper to return the next DSI bridge in the chain.
> > >
> > > Unlike general bridge return helper devm_drm_of_get_bridge, this
> > > helper uses the dsi specific panel_or_bridge helper to find the
> > > next DSI device in the pipeline.
> > >
> > > Helper lookup a given child DSI node or a DT node's port and
> > > endpoint number, find the connected node and return either
> > > the associated struct drm_panel or drm_bridge device.
> >
> > I'm not sure that using a device managed helper is the right choice
> > here. The bridge will stay longer than the backing device so it will
> > create a use-after-free. You should probably use a DRM-managed action
> > here instead.
> 
> Thanks for the comments. If I understand correctly we can use
> drmm_panel_bridge_add instead devm_drm_panel_bridge_add once we found
> the panel or bridge - am I correct?

It's not that we can, it's that the devm_panel_bridge_add is unsafe:
when the module is removed the device will go away and all the devm
resources freed, but the DRM device sticks around until the last
application with a fd open closes that fd.

Maxime