remoteproc: stm32: Properly set co-processor state when attaching

Introduce the required mechanic to set the state of the M4 in order
to properly deal with scenarios where the co-processor has been
started by another entity.

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

[1]. https://patchwork.kernel.org/project/linux-remoteproc/list/?series=239877

Acked-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20200714200445.1427257-7-mathieu.poirier@linaro.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/remoteproc/stm32_rproc.c

@@ -39,6 +39,13 @@
 #define STM32_MBX_VQ1_ID	1
 #define STM32_MBX_SHUTDOWN	"shutdown"
 
+#define M4_STATE_OFF		0
+#define M4_STATE_INI		1
+#define M4_STATE_CRUN		2
+#define M4_STATE_CSTOP		3
+#define M4_STATE_STANDBY	4
+#define M4_STATE_CRASH		5
+
 struct stm32_syscon {
 	struct regmap *map;
 	u32 reg;
@@ -636,12 +643,29 @@ static int stm32_rproc_parse_dt(struct platform_device *pdev,
 	return 0;
 }
 
+static int stm32_rproc_get_m4_status(struct stm32_rproc *ddata,
+				     unsigned int *state)
+{
+	/* See stm32_rproc_parse_dt() */
+	if (!ddata->m4_state.map) {
+		/*
+		 * We couldn't get the coprocessor's state, assume
+		 * it is not running.
+		 */
+		state = M4_STATE_OFF;
+		return 0;
+	}
+
+	return regmap_read(ddata->m4_state.map, ddata->m4_state.reg, state);
+}
+
 static int stm32_rproc_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct stm32_rproc *ddata;
 	struct device_node *np = dev->of_node;
 	struct rproc *rproc;
+	unsigned int state;
 	int ret;
 
 	ret = dma_coerce_mask_and_coherent(dev, DMA_BIT_MASK(32));
@@ -664,6 +688,13 @@ static int stm32_rproc_probe(struct platform_device *pdev)
 	if (ret)
 		goto free_rproc;
 
+	ret = stm32_rproc_get_m4_status(ddata, &state);
+	if (ret)
+		goto free_rproc;
+
+	if (state == M4_STATE_CRUN)
+		rproc->state = RPROC_DETACHED;
+
 	rproc->has_iommu = false;
 	ddata->workqueue = create_workqueue(dev_name(dev));
 	if (!ddata->workqueue) {