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

[Jagan Teki]

On Mon, Jan 30, 2023 at 6:28 PM Maxime Ripard <maxime at cerno.tech> wrote:
>
> 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.

Thanks for the details. I think this is the reason you have introduced
this DRM-managed action helper - drmm_of_get_bridge. Initially, i
thought of adding similar, but as you are aware it is not possible to
call it from the host attach.

Jagan.