soc: qcom: rpmh-rsc: Add fast-path request support

In order to support lockless RPMh request, let's dedicate a TCS for this
purpose. This TCS shall be defined as FAST_PATH_TCS in the TCS
configuration for the RSC.

The fast-path TCS will have the following properties -
- A single TCS shall be defined as a fast-path TCS.
- Fast-path TCS will not use interrupt for signalling request
  completion.
- Fast path will poll controller status for idle before sending request.
- DRV properties are not updated during the fast-path use.
- Fast path requests must be first initialized with {addr, data}.
- Subsequent updates will only update the data in the TCS and trigger.
- Requests must be fire-n-forget only (no completion).

Change-Id: I235ea60159e40affa9ce1e4069e11eca3925a423
Signed-off-by: Lina Iyer <ilina@codeaurora.org>
Signed-off-by: Maulik Shah <quic_mkshah@quicinc.com>

drivers/soc/qcom/rpmh-internal.h

@@ -11,7 +11,7 @@
 #include <linux/wait.h>
 #include <soc/qcom/tcs.h>
 
-#define TCS_TYPE_NR			4
+#define TCS_TYPE_NR			5
 #define MAX_CMDS_PER_TCS		16
 #define MAX_TCS_PER_TYPE		3
 #define MAX_TCS_NR			(MAX_TCS_PER_TYPE * TCS_TYPE_NR)
@@ -153,4 +153,9 @@ void rpmh_tx_done(const struct tcs_request *msg, int r);
 int rpmh_flush(struct rpmh_ctrlr *ctrlr);
 int _rpmh_flush(struct rpmh_ctrlr *ctrlr);
 
+int rpmh_rsc_init_fast_path(struct rsc_drv *drv, const struct tcs_request *msg);
+int rpmh_rsc_update_fast_path(struct rsc_drv *drv,
+			      const struct tcs_request *msg,
+			      u32 update_mask);
+
 #endif /* __RPM_INTERNAL_H__ */

drivers/soc/qcom/rpmh-rsc.c

@@ -876,6 +876,11 @@ static bool rpmh_rsc_ctrlr_is_busy(struct rsc_drv *drv)
 	max = tcs->offset + tcs->num_tcs;
 	set = find_next_bit(drv->tcs_in_use, max, tcs->offset);
 
+	/* Check if there is pending fastpath transaction */
+	if (drv->tcs[FAST_PATH_TCS].num_tcs &&
+	    !read_tcs_reg(drv, RSC_DRV_STATUS, drv->tcs[FAST_PATH_TCS].offset))
+		return true;
+
 	return set < max;
 }
 
@@ -985,6 +990,90 @@ int rpmh_rsc_mode_solver_set(struct rsc_drv *drv, bool enable)
 	return ret;
 }
 
+/**
+ * rpmh_rsc_init_fast_path() - Initialize the fast-path TCS contents
+ * @drv:    The controller.
+ * @msg:    The TCS request to populate.
+ *
+ * Return:
+ * * 0			- success
+ * * -ENODEV            - no fast-path TCS available
+ */
+int rpmh_rsc_init_fast_path(struct rsc_drv *drv, const struct tcs_request *msg)
+{
+	int tcs_id;
+
+	if (!drv->tcs[FAST_PATH_TCS].num_tcs)
+		return -ENODEV;
+
+	tcs_id = drv->tcs[FAST_PATH_TCS].offset;
+
+	/* We won't use the AMC IRQ to confirm if the TCS is free */
+	enable_tcs_irq(drv, tcs_id, false);
+
+	__tcs_buffer_write(drv, tcs_id, 0, msg);
+
+	return 0;
+}
+
+/**
+ * rpmh_rsc_update_fast_path() - Update the fast-path TCS data and trigger
+ * @drv:     The controller.
+ * @msg:     The TCS request data to be updated.
+ * @mask:    The update mask for elements in @msg to be sent
+ *
+ * NOTE: Caller should ensure serialization before making this call.
+ * Return:
+ * * 0			- success
+ * * -ENODEV            - no fast-path TCS available
+ */
+int rpmh_rsc_update_fast_path(struct rsc_drv *drv,
+			      const struct tcs_request *msg,
+			      u32 mask)
+{
+	int i;
+	u32 sts;
+	int tcs_id;
+	struct tcs_cmd *cmd;
+	int retry = 5;
+
+	if (!drv->tcs[FAST_PATH_TCS].num_tcs)
+		return -ENODEV;
+
+	tcs_id = drv->tcs[FAST_PATH_TCS].offset;
+
+	/* Ensure the TCS is free before writing to the TCS */
+	do {
+		sts = read_tcs_reg(drv, RSC_DRV_STATUS, tcs_id);
+		if (!sts) {
+			retry--;
+			/* Report and bail, if it took too many attempts */
+			if (!retry) {
+				pr_err("Fast-path TCS is too busy\n");
+				return -EBUSY;
+			}
+			udelay(1);
+		}
+	} while (!sts);
+
+	/*
+	 * We only update the data, everything else remains the same.
+	 * The number of commands and the addresses do not change with
+	 * updates.
+	 */
+	for (i = 0; i < msg->num_cmds; i++) {
+		if (!(mask & BIT(i)))
+			continue;
+		cmd = &msg->cmds[i];
+		write_tcs_cmd(drv, RSC_DRV_CMD_DATA, tcs_id, i, cmd->data);
+	}
+
+	/* Trigger the TCS to send the request */
+	__tcs_set_trigger(drv, tcs_id, true);
+
+	return 0;
+}
+
 static int rpmh_probe_tcs_config(struct platform_device *pdev,
 				 struct rsc_drv *drv, void __iomem *base)
 {