On Tue, Jan 31, 2023 at 6:16 PM Maxime Ripard <maxime@xxxxxxxxxx> wrote: > > On Mon, Jan 30, 2023 at 06:54:54PM +0530, Jagan Teki wrote: > > On Mon, Jan 30, 2023 at 6:26 PM Maxime Ripard <maxime@xxxxxxxxxx> wrote: > > > > > > 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@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > On Thu, Jan 26, 2023 at 5:42 PM Maxime Ripard <maxime@xxxxxxxxxx> 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 > > > > True, If I remember we have bridges earlier to find the downstream > > bridge/panels from the bridge ops and attach the hook, if that is the > > case maybe we can use this DRM-managed action as we can get the > > drm_device pointer from the bridge pointer. > > I'm not quite sure what you mean. You shouldn't retrieve the bridge from > the attach hook but from the probe / bind ones. If that's not working > for you, this is a bug in the documentation we should address. Something like this, afterward the design has updated to move the panel or bridge found to be in host attach. https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/gpu/drm/bridge/nwl-dsi.c?h=v5.10#n911 > > > So, what is the best we can do here, add any TODO comment to follow up > > the same in the future or something else, please let me know? > > Make it work in a safe way, as described in the documentation? Yeah, it is a clear deadlock. It is not possible to use DM-managed action helper in host attach as there is no drm_device pointer and we cannot move panel or bridge finding out of host attach as per design documentation. I'm thinking of go-ahead with adding TODO for adding the safe way with an existing patch. Please let me know. Thanks, Jagan.
