libcamera: raspberrypi: Document vc_sm_cma pointer sharing with IPA

Sharing a pointer with the IPA is fragile as it will not work with all
IPC mechanisms. Document that it's a temporary workaround that should be
reworked.

Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/pipeline/raspberrypi/raspberrypi.cpp

@@ -1014,6 +1014,11 @@ int PipelineHandlerRPi::configureIPA(Camera *camera)
 		/*
 		 * The vcsm allocation will always be in the memory region
 		 * < 32-bits to allow Videocore to access the memory.
+		 *
+		 * \todo Sending a pointer to the IPA is a workaround for
+		 * vc_sm_cma not yet supporting dmabuf. This will not work with
+		 * IPA module isolation and should be reworked when vc_sma_cma
+		 * will permit.
 		 */
 		IPAOperationData op;
 		op.operation = RPI_IPA_EVENT_LS_TABLE_ALLOCATION;