tee: system session

Adds kernel client API function tee_client_system_session() for a client
to request a system service entry in TEE context.

This feature is needed to prevent a system deadlock when several TEE
client applications invoke TEE, consuming all TEE thread contexts
available in the secure world. The deadlock can happen in the OP-TEE
driver for example if all these TEE threads issue an RPC call from TEE
to Linux OS to access an eMMC RPMB partition (TEE secure storage) which
device clock or regulator controller is accessed through an OP-TEE SCMI
services. In that case, Linux SCMI driver must reach OP-TEE SCMI service
without waiting until one of the consumed TEE threads is freed.

Reviewed-by: Sumit Garg <[e-mail]>
Co-developed-by: Jens Wiklander <[e-mail]>
Signed-off-by: Etienne Carriere <[e-mail]>
Signed-off-by: Jens Wiklander <[e-mail]>

drivers/tee/tee_core.c

···
 }
 EXPORT_SYMBOL_GPL(tee_client_close_session);
 
+int tee_client_system_session(struct tee_context *ctx, u32 session)
+{
+	if (!ctx->teedev->desc->ops->system_session)
+		return -EINVAL;
+	return ctx->teedev->desc->ops->system_session(ctx, session);
+}
+EXPORT_SYMBOL_GPL(tee_client_system_session);
+
 int tee_client_invoke_func(struct tee_context *ctx,
 			   struct tee_ioctl_invoke_arg *arg,
 			   struct tee_param *param)

include/linux/tee_drv.h

···
  * @release:		release this open file
  * @open_session:	open a new session
  * @close_session:	close a session
+ * @system_session:	declare session as a system session
  * @invoke_func:	invoke a trusted function
  * @cancel_req:		request cancel of an ongoing invoke or open
  * @supp_recv:		called for supplicant to get a command
···
 			    struct tee_ioctl_open_session_arg *arg,
 			    struct tee_param *param);
 	int (*close_session)(struct tee_context *ctx, u32 session);
+	int (*system_session)(struct tee_context *ctx, u32 session);
 	int (*invoke_func)(struct tee_context *ctx,
 			   struct tee_ioctl_invoke_arg *arg,
 			   struct tee_param *param);
···
  * valid after this function has returned.
  */
 int tee_client_close_session(struct tee_context *ctx, u32 session);
+
+/**
+ * tee_client_system_session() - Declare session as a system session
+ * @ctx:	TEE Context
+ * @session:	Session id
+ *
+ * This function requests TEE to provision an entry context ready to use for
+ * that session only. The provisioned entry context is used for command
+ * invocation and session closure, not for command cancelling requests.
+ * TEE releases the provisioned context upon session closure.
+ *
+ * Return < 0 on error else 0 if an entry context has been provisioned.
+ */
+int tee_client_system_session(struct tee_context *ctx, u32 session);
 
 /**
  * tee_client_invoke_func() - Invoke a function in a Trusted Application