firmware: arm_scmi: Augment SMC/HVC to allow optional parameters

This change adds support for passing shmem channel address as parameters
in smc/hvc call. The address is split into 4KB-page and offset.
This is useful when multiple scmi instances are using same smc-id
and firmware needs to distinguish among the instances.

Signed-off-by: Nikunj Kela <quic_nkela@quicinc.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20230506182428.25343-3-quic_nkela@quicinc.com
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

Author: Nikunj Kela

drivers/firmware/arm_scmi/driver.c

@@ -2914,6 +2914,7 @@ static const struct of_device_id scmi_of_match[] = {
 #endif
 #ifdef CONFIG_ARM_SCMI_TRANSPORT_SMC
 	{ .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
+	{ .compatible = "arm,scmi-smc-param", .data = &scmi_smc_desc},
 #endif
 #ifdef CONFIG_ARM_SCMI_TRANSPORT_VIRTIO
 	{ .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},

drivers/firmware/arm_scmi/smc.c

@@ -20,6 +20,23 @@
 
 #include "common.h"
 
+/*
+ * The shmem address is split into 4K page and offset.
+ * This is to make sure the parameters fit in 32bit arguments of the
+ * smc/hvc call to keep it uniform across smc32/smc64 conventions.
+ * This however limits the shmem address to 44 bit.
+ *
+ * These optional parameters can be used to distinguish among multiple
+ * scmi instances that are using the same smc-id.
+ * The page parameter is passed in r1/x1/w1 register and the offset parameter
+ * is passed in r2/x2/w2 register.
+ */
+
+#define SHMEM_SIZE (SZ_4K)
+#define SHMEM_SHIFT 12
+#define SHMEM_PAGE(x) (_UL((x) >> SHMEM_SHIFT))
+#define SHMEM_OFFSET(x) ((x) & (SHMEM_SIZE - 1))
+
 /**
  * struct scmi_smc - Structure representing a SCMI smc transport
  *
@@ -30,6 +47,8 @@
  * @inflight: Atomic flag to protect access to Tx/Rx shared memory area.
  *	      Used when operating in atomic mode.
  * @func_id: smc/hvc call function id
+ * @param_page: 4K page number of the shmem channel
+ * @param_offset: Offset within the 4K page of the shmem channel
  */
 
 struct scmi_smc {
@@ -40,6 +59,8 @@ struct scmi_smc {
 #define INFLIGHT_NONE	MSG_TOKEN_MAX
 	atomic_t inflight;
 	u32 func_id;
+	u32 param_page;
+	u32 param_offset;
 };
 
 static irqreturn_t smc_msg_done_isr(int irq, void *data)
@@ -137,6 +158,10 @@ static int smc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
 	if (ret < 0)
 		return ret;
 
+	if (of_device_is_compatible(dev->of_node, "arm,scmi-smc-param")) {
+		scmi_info->param_page = SHMEM_PAGE(res.start);
+		scmi_info->param_offset = SHMEM_OFFSET(res.start);
+	}
 	/*
 	 * If there is an interrupt named "a2p", then the service and
 	 * completion of a message is signaled by an interrupt rather than by
@@ -179,6 +204,8 @@ static int smc_send_message(struct scmi_chan_info *cinfo,
 {
 	struct scmi_smc *scmi_info = cinfo->transport_info;
 	struct arm_smccc_res res;
+	unsigned long page = scmi_info->param_page;
+	unsigned long offset = scmi_info->param_offset;
 
 	/*
 	 * Channel will be released only once response has been
@@ -188,7 +215,8 @@ static int smc_send_message(struct scmi_chan_info *cinfo,
 
 	shmem_tx_prepare(scmi_info->shmem, xfer, cinfo);
 
-	arm_smccc_1_1_invoke(scmi_info->func_id, 0, 0, 0, 0, 0, 0, 0, &res);
+	arm_smccc_1_1_invoke(scmi_info->func_id, page, offset, 0, 0, 0, 0, 0,
+			     &res);
 
 	/* Only SMCCC_RET_NOT_SUPPORTED is valid error code */
 	if (res.a0) {