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

[Maxime Ripard]

On Fri, Jan 27, 2023 at 11:09:26PM +0530, Jagan Teki wrote:
> Hi,
> 
> On Thu, Jan 26, 2023 at 8:48 PM Jagan Teki <jagan at amarulasolutions.com> 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?
> 
> Look like it is not possible to use DRM-managed action helper here as
> devm_drm_of_dsi_get_bridge is calling from the DSI host attach hook in
> which we cannot find drm_device pointer (as drm_device pointer is
> mandatory for using DRM-managed action).
> https://github.com/openedev/kernel/blob/imx8mm-dsi-v12/drivers/gpu/drm/bridge/samsung-dsim.c#L1545
> 
> Please check and correct me if I mentioned any incorrect details.

You shouldn't call that function from attach anyway:
https://dri.freedesktop.org/docs/drm/gpu/drm-kms-helpers.html#special-care-with-mipi-dsi-bridges

Maxime