nvmem: stm32: detect bsec pta presence for STM32MP15x

On STM32MP15x SoC, the SMC backend is optional when OP-TEE is used;
the PTA BSEC should be used as it is done on STM32MP13x platform,
but the BSEC SMC can be also used: it is a legacy mode in OP-TEE,
not recommended but used in previous OP-TEE firmware.

The presence of OP-TEE is dynamically detected in STM32MP15x device tree
and the supported NVMEM backend is dynamically detected:
- PTA with stm32_bsec_pta_find
- SMC with stm32_bsec_check

With OP-TEE but without PTA and SMC detection, the probe is deferred for
STM32MP15x devices.

On STM32MP13x platform, only the PTA is supported with cfg->ta = true
and this detection is skipped.
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Etienne Carriere <etienne.carriere@linaro.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20230206134356.839737-19-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/stm32-romem.c

@@ -159,6 +159,31 @@ static int stm32_bsec_pta_write(void *context, unsigned int offset, void *buf,
 	return stm32_bsec_optee_ta_write(priv->ctx, priv->lower, offset, buf, bytes);
 }
 
+static bool stm32_bsec_smc_check(void)
+{
+	u32 val;
+	int ret;
+
+	/* check that the OP-TEE support the BSEC SMC (legacy mode) */
+	ret = stm32_bsec_smc(STM32_SMC_READ_SHADOW, 0, 0, &val);
+
+	return !ret;
+}
+
+static bool optee_presence_check(void)
+{
+	struct device_node *np;
+	bool tee_detected = false;
+
+	/* check that the OP-TEE node is present and available. */
+	np = of_find_compatible_node(NULL, NULL, "linaro,optee-tz");
+	if (np && of_device_is_available(np))
+		tee_detected = true;
+	of_node_put(np);
+
+	return tee_detected;
+}
+
 static int stm32_romem_probe(struct platform_device *pdev)
 {
 	const struct stm32_romem_cfg *cfg;
@@ -195,11 +220,16 @@ static int stm32_romem_probe(struct platform_device *pdev)
 	} else {
 		priv->cfg.size = cfg->size;
 		priv->lower = cfg->lower;
-		if (cfg->ta) {
+		if (cfg->ta || optee_presence_check()) {
 			rc = stm32_bsec_optee_ta_open(&priv->ctx);
-			/* wait for OP-TEE client driver to be up and ready */
-			if (rc)
-				return rc;
+			if (rc) {
+				/* wait for OP-TEE client driver to be up and ready */
+				if (rc == -EPROBE_DEFER)
+					return -EPROBE_DEFER;
+				/* BSEC PTA is required or SMC not supported */
+				if (cfg->ta || !stm32_bsec_smc_check())
+					return rc;
+			}
 		}
 		if (priv->ctx) {
 			rc = devm_add_action_or_reset(dev, stm32_bsec_optee_ta_close, priv->ctx);