remoteproc: stm32: add capability to detach

A mechanism similar to the shutdown mailbox signal is implemented to
detach a remote processor.

Upon detachment, a signal is sent to the remote firmware, allowing it
to perform specific actions such as stopping rpmsg communication.

The Cortex-M hold boot is also disabled to allow the remote processor
to restart in case of crash.
Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Tested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20210331073347.8293-3-arnaud.pouliquen@foss.st.comSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/remoteproc/stm32_rproc.c

@@ -28,7 +28,7 @@
 #define RELEASE_BOOT		1
 
 #define MBOX_NB_VQ		2
-#define MBOX_NB_MBX		3
+#define MBOX_NB_MBX		4
 
 #define STM32_SMC_RCC		0x82001000
 #define STM32_SMC_REG_WRITE	0x1
@@ -38,6 +38,7 @@
 #define STM32_MBX_VQ1		"vq1"
 #define STM32_MBX_VQ1_ID	1
 #define STM32_MBX_SHUTDOWN	"shutdown"
+#define STM32_MBX_DETACH	"detach"
 
 #define RSC_TBL_SIZE		1024
 
@@ -336,6 +337,15 @@ static const struct stm32_mbox stm32_rproc_mbox[MBOX_NB_MBX] = {
 			.tx_done = NULL,
 			.tx_tout = 500, /* 500 ms time out */
 		},
+	},
+	{
+		.name = STM32_MBX_DETACH,
+		.vq_id = -1,
+		.client = {
+			.tx_block = true,
+			.tx_done = NULL,
+			.tx_tout = 200, /* 200 ms time out to detach should be fair enough */
+		},
 	}
 };
 
@@ -461,6 +471,25 @@ static int stm32_rproc_attach(struct rproc *rproc)
 	return stm32_rproc_set_hold_boot(rproc, true);
 }
 
+static int stm32_rproc_detach(struct rproc *rproc)
+{
+	struct stm32_rproc *ddata = rproc->priv;
+	int err, dummy_data, idx;
+
+	/* Inform the remote processor of the detach */
+	idx = stm32_rproc_mbox_idx(rproc, STM32_MBX_DETACH);
+	if (idx >= 0 && ddata->mb[idx].chan) {
+		/* A dummy data is sent to allow to block on transmit */
+		err = mbox_send_message(ddata->mb[idx].chan,
+					&dummy_data);
+		if (err < 0)
+			dev_warn(&rproc->dev, "warning: remote FW detach without ack\n");
+	}
+
+	/* Allow remote processor to auto-reboot */
+	return stm32_rproc_set_hold_boot(rproc, false);
+}
+
 static int stm32_rproc_stop(struct rproc *rproc)
 {
 	struct stm32_rproc *ddata = rproc->priv;
@@ -597,7 +626,12 @@ stm32_rproc_get_loaded_rsc_table(struct rproc *rproc, size_t *table_sz)
 	}
 
 done:
-	/* Assuming the resource table fits in 1kB is fair */
+	/*
+	 * Assuming the resource table fits in 1kB is fair.
+	 * Notice for the detach, that this 1 kB memory area has to be reserved in the coprocessor
+	 * firmware for the resource table. On detach, the remoteproc core re-initializes this
+	 * entire area by overwriting it with the initial values stored in rproc->clean_table.
+	 */
 	*table_sz = RSC_TBL_SIZE;
 	return (struct resource_table *)ddata->rsc_va;
 }
@@ -607,6 +641,7 @@ static const struct rproc_ops st_rproc_ops = {
 	.start		= stm32_rproc_start,
 	.stop		= stm32_rproc_stop,
 	.attach		= stm32_rproc_attach,
+	.detach		= stm32_rproc_detach,
 	.kick		= stm32_rproc_kick,
 	.load		= rproc_elf_load_segments,
 	.parse_fw	= stm32_rproc_parse_fw,