remoteproc: stm32: Allow hold boot management by the SCMI reset controller

The hold boot can be managed by the SCMI controller as a reset.
If the "hold_boot" reset is defined in the device tree, use it.
Else use the syscon controller directly to access to the register.
The support of the SMC call is deprecated but kept for legacy support.
Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Link: https://lore.kernel.org/r/20230512093926.661509-3-arnaud.pouliquen@foss.st.com

drivers/remoteproc/stm32_rproc.c

@@ -79,6 +79,7 @@ struct stm32_mbox {
 
 struct stm32_rproc {
 	struct reset_control *rst;
+	struct reset_control *hold_boot_rst;
 	struct stm32_syscon hold_boot;
 	struct stm32_syscon pdds;
 	struct stm32_syscon m4_state;
@@ -88,7 +89,7 @@ struct stm32_rproc {
 	struct stm32_rproc_mem *rmems;
 	struct stm32_mbox mb[MBOX_NB_MBX];
 	struct workqueue_struct *workqueue;
-	bool secured_soc;
+	bool hold_boot_smc;
 	void __iomem *rsc_va;
 };
 
@@ -413,13 +414,28 @@ static int stm32_rproc_set_hold_boot(struct rproc *rproc, bool hold)
 	struct arm_smccc_res smc_res;
 	int val, err;
 
+	/*
+	 * Three ways to manage the hold boot
+	 * - using SCMI: the hold boot is managed as a reset,
+	 * - using Linux(no SCMI): the hold boot is managed as a syscon register
+	 * - using SMC call (deprecated): use SMC reset interface
+	 */
+
 	val = hold ? HOLD_BOOT : RELEASE_BOOT;
 
-	if (IS_ENABLED(CONFIG_HAVE_ARM_SMCCC) && ddata->secured_soc) {
+	if (ddata->hold_boot_rst) {
+		/* Use the SCMI reset controller */
+		if (!hold)
+			err = reset_control_deassert(ddata->hold_boot_rst);
+		else
+			err =  reset_control_assert(ddata->hold_boot_rst);
+	} else if (IS_ENABLED(CONFIG_HAVE_ARM_SMCCC) && ddata->hold_boot_smc) {
+		/* Use the SMC call */
 		arm_smccc_smc(STM32_SMC_RCC, STM32_SMC_REG_WRITE,
 			      hold_boot.reg, val, 0, 0, 0, 0, &smc_res);
 		err = smc_res.a0;
 	} else {
+		/* Use syscon */
 		err = regmap_update_bits(hold_boot.map, hold_boot.reg,
 					 hold_boot.mask, val);
 	}
@@ -717,35 +733,53 @@ static int stm32_rproc_parse_dt(struct platform_device *pdev,
 		dev_info(dev, "wdg irq registered\n");
 	}
 
+	ddata->rst = devm_reset_control_get_optional(dev, "mcu_rst");
+	if (!ddata->rst) {
+		/* Try legacy fallback method: get it by index */
 		ddata->rst = devm_reset_control_get_by_index(dev, 0);
+	}
 	if (IS_ERR(ddata->rst))
 		return dev_err_probe(dev, PTR_ERR(ddata->rst),
 				     "failed to get mcu_reset\n");
 
 	/*
-	 * if platform is secured the hold boot bit must be written by
-	 * smc call and read normally.
-	 * if not secure the hold boot bit could be read/write normally
+	 * Three ways to manage the hold boot
+	 * - using SCMI: the hold boot is managed as a reset
+	 *    The DT "reset-mames" property should be defined with 2 items:
+	 *        reset-names = "mcu_rst", "hold_boot";
+	 * - using SMC call (deprecated): use SMC reset interface
+	 *    The DT "reset-mames" property is optional, "st,syscfg-tz" is required
+	 * - default(no SCMI, no SMC): the hold boot is managed as a syscon register
+	 *    The DT "reset-mames" property is optional, "st,syscfg-holdboot" is required
 	 */
-	err = stm32_rproc_get_syscon(np, "st,syscfg-tz", &tz);
-	if (err) {
-		dev_err(dev, "failed to get tz syscfg\n");
-		return err;
-	}
 
+	ddata->hold_boot_rst = devm_reset_control_get_optional(dev, "hold_boot");
+	if (IS_ERR(ddata->hold_boot_rst))
+		return dev_err_probe(dev, PTR_ERR(ddata->rst),
+				     "failed to get hold_boot reset\n");
+
+	if (!ddata->hold_boot_rst && IS_ENABLED(CONFIG_HAVE_ARM_SMCCC)) {
+		/* Manage the MCU_BOOT using SMC call */
+		err = stm32_rproc_get_syscon(np, "st,syscfg-tz", &tz);
+		if (!err) {
 			err = regmap_read(tz.map, tz.reg, &tzen);
 			if (err) {
 				dev_err(dev, "failed to read tzen\n");
 				return err;
 			}
-	ddata->secured_soc = tzen & tz.mask;
+			ddata->hold_boot_smc = tzen & tz.mask;
+		}
+	}
 
+	if (!ddata->hold_boot_rst && !ddata->hold_boot_smc) {
+		/* Default: hold boot manage it through the syscon controller */
 		err = stm32_rproc_get_syscon(np, "st,syscfg-holdboot",
 					     &ddata->hold_boot);
 		if (err) {
 			dev_err(dev, "failed to get hold boot\n");
 			return err;
 		}
+	}
 
 	err = stm32_rproc_get_syscon(np, "st,syscfg-pdds", &ddata->pdds);
 	if (err)