From 7e26d3ef3ffa11e7c5b80b81ee2daba28689cd0d Mon Sep 17 00:00:00 2001
From: Norman Feske <norman.feske@genode-labs.com>
Date: Thu, 3 Feb 2022 15:47:29 +0100
Subject: [PATCH] Give diagnostic aid to callers of 'dma_addr'

If the platform driver lacks the 'managing_system="yes"' attribute,
requests for DMA addresses return 0. This patch is meant to help
diagnosing such configuration issues.

Issue #2243
---
 repos/os/include/platform_session/client.h | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/repos/os/include/platform_session/client.h b/repos/os/include/platform_session/client.h
index 08803b7a35..fa96596d17 100644
--- a/repos/os/include/platform_session/client.h
+++ b/repos/os/include/platform_session/client.h
@@ -15,6 +15,7 @@
 #define _INCLUDE__PLATFORM_SESSION__CLIENT_H_
 
 #include <base/rpc_client.h>
+#include <base/log.h>
 #include <platform_session/capability.h>
 
 namespace Platform { struct Client; }
@@ -43,8 +44,16 @@ struct Platform::Client : Genode::Rpc_client<Session>
 	void free_dma_buffer(Ram_dataspace_capability cap) override {
 		call<Rpc_free_dma_buffer>(cap); }
 
-	addr_t dma_addr(Ram_dataspace_capability cap) override {
-		return call<Rpc_dma_addr>(cap); }
+	addr_t dma_addr(Ram_dataspace_capability cap) override
+	{
+		addr_t const result = call<Rpc_dma_addr>(cap);
+
+		/* the platform driver may lack the 'managing_system' role */
+		if (!result)
+			warning("unable to obtain DMA address from platform driver");
+
+		return result;
+	}
 };
 
 #endif /* _INCLUDE__PLATFORM_SESSION__CLIENT_H_ */