[PATCH v7 02/23] firmware: arm_scmi: Allow registration of unknown-size events/reports

[Cristian Marussi <cristian.marussi@arm.com>]

Allow protocols to register events with build-time unknown sizes: such
events can be declared zero-sized and let the core SCMI stack perform the
needed safe-net boundary checks based on the configured transport size.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
v2 --> v3
 - split out of previous patch on protocol notifier
 - use max() instead of max_t()
---
 drivers/firmware/arm_scmi/notify.c | 24 +++++++++++++++++++-----
 drivers/firmware/arm_scmi/notify.h |  8 ++++++--
 2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/drivers/firmware/arm_scmi/notify.c b/drivers/firmware/arm_scmi/notify.c
index 0a192cf2deab..8995dd1b12aa 100644
--- a/drivers/firmware/arm_scmi/notify.c
+++ b/drivers/firmware/arm_scmi/notify.c
@@ -595,7 +595,13 @@ int scmi_notify(const struct scmi_handle *handle, u8 proto_id, u8 evt_id,
 	if (!r_evt)
 		return -EINVAL;
 
-	if (len > r_evt->evt->max_payld_sz) {
+	/*
+	 * Events with a zero max_payld_sz are sized to be of the maximum
+	 * size allowed by the transport: no need to be size-checked here
+	 * since the transport layer would have already dropped such
+	 * over-sized messages.
+	 */
+	if (r_evt->evt->max_payld_sz && len > r_evt->evt->max_payld_sz) {
 		dev_err(handle->dev, "discard badly sized message\n");
 		return -EINVAL;
 	}
@@ -754,7 +760,7 @@ int scmi_register_protocol_events(const struct scmi_handle *handle, u8 proto_id,
 				  const struct scmi_protocol_handle *ph,
 				  const struct scmi_protocol_events *ee)
 {
-	int i;
+	int i, max_msg_sz;
 	unsigned int num_sources;
 	size_t payld_sz = 0;
 	struct scmi_registered_events_desc *pd;
@@ -769,6 +775,8 @@ int scmi_register_protocol_events(const struct scmi_handle *handle, u8 proto_id,
 	if (!ni)
 		return -ENOMEM;
 
+	max_msg_sz = ph->hops->get_max_msg_size(ph);
+
 	/* num_sources cannot be <= 0 */
 	if (ee->num_sources) {
 		num_sources = ee->num_sources;
@@ -781,8 +789,13 @@ int scmi_register_protocol_events(const struct scmi_handle *handle, u8 proto_id,
 	}
 
 	evt = ee->evts;
-	for (i = 0; i < ee->num_events; i++)
-		payld_sz = max_t(size_t, payld_sz, evt[i].max_payld_sz);
+	for (i = 0; i < ee->num_events; i++) {
+		if (evt[i].max_payld_sz == 0) {
+			payld_sz = max_msg_sz;
+			break;
+		}
+		payld_sz = max(payld_sz, evt[i].max_payld_sz);
+	}
 	payld_sz += sizeof(struct scmi_event_header);
 
 	pd = scmi_allocate_registered_events_desc(ni, proto_id, ee->queue_sz,
@@ -811,7 +824,8 @@ int scmi_register_protocol_events(const struct scmi_handle *handle, u8 proto_id,
 		mutex_init(&r_evt->sources_mtx);
 
 		r_evt->report = devm_kzalloc(ni->handle->dev,
-					     evt->max_report_sz, GFP_KERNEL);
+					     evt->max_report_sz ?: max_msg_sz,
+					     GFP_KERNEL);
 		if (!r_evt->report)
 			return -ENOMEM;
 
diff --git a/drivers/firmware/arm_scmi/notify.h b/drivers/firmware/arm_scmi/notify.h
index 76758a736cf4..ecfa4b746487 100644
--- a/drivers/firmware/arm_scmi/notify.h
+++ b/drivers/firmware/arm_scmi/notify.h
@@ -18,8 +18,12 @@
 /**
  * struct scmi_event  - Describes an event to be supported
  * @id: Event ID
- * @max_payld_sz: Max possible size for the payload of a notification message
- * @max_report_sz: Max possible size for the report of a notification message
+ * @max_payld_sz: Max possible size for the payload of a notification message.
+ *		  Set to zero to use the maximum payload size allowed by the
+ *		  transport.
+ * @max_report_sz: Max possible size for the report of a notification message.
+ *		  Set to zero to use the maximum payload size allowed by the
+ *		  transport.
  *
  * Each SCMI protocol, during its initialization phase, can describe the events
  * it wishes to support in a few struct scmi_event and pass them to the core
-- 
2.54.0