firmware: arm_scmi: Use asynchronous CLOCK_RATE_SET when possible

CLOCK_PROTOCOL_ATTRIBUTES provides attributes to indicate the maximum
number of pending asynchronous clock rate changes supported by the
platform. If it's non-zero, then we should be able to use asynchronous
clock rate set for any clocks until the maximum limit is reached.

Tracking the current count of pending asynchronous clock set rate
requests, we can decide if the incoming/new request for clock set rate
can be handled asynchronously or not until the maximum limit is
reached.

Cc: [e-mail]
Reviewed-by: Stephen Boyd <[e-mail]>
Signed-off-by: Sudeep Holla <[e-mail]>

drivers/firmware/arm_scmi/clock.c

···
 struct scmi_clock_set_rate {
 	__le32 flags;
 #define CLOCK_SET_ASYNC		BIT(0)
-#define CLOCK_SET_DELAYED	BIT(1)
+#define CLOCK_SET_IGNORE_RESP	BIT(1)
 #define CLOCK_SET_ROUND_UP	BIT(2)
 #define CLOCK_SET_ROUND_AUTO	BIT(3)
 	__le32 id;
···
 struct clock_info {
 	int num_clocks;
 	int max_async_req;
+	atomic_t cur_async_req;
 	struct scmi_clock_info *clk;
 };
 
···
 			       u64 rate)
 {
 	int ret;
+	u32 flags = 0;
 	struct scmi_xfer *t;
 	struct scmi_clock_set_rate *cfg;
+	struct clock_info *ci = handle->clk_priv;
 
 	ret = scmi_xfer_get_init(handle, CLOCK_RATE_SET, SCMI_PROTOCOL_CLOCK,
 				 sizeof(*cfg), 0, &t);
 	if (ret)
 		return ret;
 
+	if (ci->max_async_req &&
+	    atomic_inc_return(&ci->cur_async_req) < ci->max_async_req)
+		flags |= CLOCK_SET_ASYNC;
+
 	cfg = t->tx.buf;
-	cfg->flags = cpu_to_le32(0);
+	cfg->flags = cpu_to_le32(flags);
 	cfg->id = cpu_to_le32(clk_id);
 	cfg->value_low = cpu_to_le32(rate & 0xffffffff);
 	cfg->value_high = cpu_to_le32(rate >> 32);
 
-	ret = scmi_do_xfer(handle, t);
+	if (flags & CLOCK_SET_ASYNC)
+		ret = scmi_do_xfer_with_response(handle, t);
+	else
+		ret = scmi_do_xfer(handle, t);
+
+	if (ci->max_async_req)
+		atomic_dec(&ci->cur_async_req);
 
 	scmi_xfer_put(handle, t);
 	return ret;