remoteproc: stm32: Update M4 state in stm32_rproc_stop()

Update the co-processor state in function stm32_rproc_stop() so that
it can be used in scenarios where the remoteproc core is attaching
to the M4.

Mainly based on the work published by Arnaud Pouliquen [1].

[1]. https://patchwork.kernel.org/project/linux-remoteproc/list/?series=239877Acked-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Link: https://lore.kernel.org/r/20200714200445.1427257-12-mathieu.poirier@linaro.orgSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/remoteproc/stm32_rproc.c

@@ -504,6 +504,18 @@ static int stm32_rproc_stop(struct rproc *rproc)
 		}
 	}
 
+	/* update coprocessor state to OFF if available */
+	if (ddata->m4_state.map) {
+		err = regmap_update_bits(ddata->m4_state.map,
+					 ddata->m4_state.reg,
+					 ddata->m4_state.mask,
+					 M4_STATE_OFF);
+		if (err) {
+			dev_err(&rproc->dev, "failed to set copro state\n");
+			return err;
+		}
+	}
+
 	return 0;
 }