firmware: arm_scmi: Relax CLOCK_DESCRIBE_RATES out-of-spec checks

A reply to CLOCK_DESCRIBE_RATES issued against a non rate-discrete clock
should be composed of a triplet of rates descriptors (min/max/step)
returned all in one reply message.

This is not always the case when dealing with some SCMI server deployed in
the wild: relax such constraint while maintaining memory safety by checking
carefully the returned payload size.

While at that cleanup a stale debug printout.

Link: https://lore.kernel.org/r/20220616170347.2800771-1-cristian.marussi@arm.com
Fixes: 7bc7caaf ("firmware: arm_scmi: Use common iterators in the clock protocol")
Tested-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/clock.c

@@ -194,6 +194,7 @@ static int rate_cmp_func(const void *_r1, const void *_r2)
 }
 
 struct scmi_clk_ipriv {
+	struct device *dev;
 	u32 clk_id;
 	struct scmi_clock_info *clk;
 };
@@ -223,6 +224,29 @@ iter_clk_describe_update_state(struct scmi_iterator_state *st,
 	st->num_returned = NUM_RETURNED(flags);
 	p->clk->rate_discrete = RATE_DISCRETE(flags);
 
+	/* Warn about out of spec replies ... */
+	if (!p->clk->rate_discrete &&
+	    (st->num_returned != 3 || st->num_remaining != 0)) {
+		dev_warn(p->dev,
+			 "Out-of-spec CLOCK_DESCRIBE_RATES reply for %s - returned:%d remaining:%d rx_len:%zd\n",
+			 p->clk->name, st->num_returned, st->num_remaining,
+			 st->rx_len);
+
+		/*
+		 * A known quirk: a triplet is returned but num_returned != 3
+		 * Check for a safe payload size and fix.
+		 */
+		if (st->num_returned != 3 && st->num_remaining == 0 &&
+		    st->rx_len == sizeof(*r) + sizeof(__le32) * 2 * 3) {
+			st->num_returned = 3;
+			st->num_remaining = 0;
+		} else {
+			dev_err(p->dev,
+				"Cannot fix out-of-spec reply !\n");
+			return -EPROTO;
+		}
+	}
+
 	return 0;
 }
 
@@ -255,7 +279,6 @@ iter_clk_describe_process_response(const struct scmi_protocol_handle *ph,
 
 		*rate = RATE_TO_U64(r->rate[st->loop_idx]);
 		p->clk->list.num_rates++;
-		//XXX dev_dbg(ph->dev, "Rate %llu Hz\n", *rate);
 	}
 
 	return ret;
@@ -275,6 +298,7 @@ scmi_clock_describe_rates_get(const struct scmi_protocol_handle *ph, u32 clk_id,
 	struct scmi_clk_ipriv cpriv = {
 		.clk_id = clk_id,
 		.clk = clk,
+		.dev = ph->dev,
 	};
 
 	iter = ph->hops->iter_response_init(ph, &ops, SCMI_MAX_NUM_RATES,

drivers/firmware/arm_scmi/driver.c

@@ -1223,6 +1223,7 @@ static int scmi_iterator_run(void *iter)
 		if (ret)
 			break;
 
+		st->rx_len = i->t->rx.len;
 		ret = iops->update_state(st, i->resp, i->priv);
 		if (ret)
 			break;

drivers/firmware/arm_scmi/protocols.h

@@ -179,6 +179,8 @@ struct scmi_protocol_handle {
  * @max_resources: Maximum acceptable number of items, configured by the caller
  *		   depending on the underlying resources that it is querying.
  * @loop_idx: The iterator loop index in the current multi-part reply.
+ * @rx_len: Size in bytes of the currenly processed message; it can be used by
+ *	    the user of the iterator to verify a reply size.
  * @priv: Optional pointer to some additional state-related private data setup
  *	  by the caller during the iterations.
  */
@@ -188,6 +190,7 @@ struct scmi_iterator_state {
 	unsigned int num_remaining;
 	unsigned int max_resources;
 	unsigned int loop_idx;
+	size_t rx_len;
 	void *priv;
 };