gpu: introduce mapping attributes

The various mapping methods are modelled after the requirements of
the Intel GPUs or rather the Mesa driver back end.

With upcoming support for other driver back ends, we need to
sequeeze their requirements in as well. For now hijack 'map_buffer'
to provide for specifying the kind of attributes the client needs.

For now all buffers mapped in the GGTT for Intel GPUs are treated
as RW.

Issue #4265.

repos/libports/src/lib/libdrm/ioctl_iris.cc

@@ -340,7 +340,8 @@ class Drm_call
 
 			try {
 				_gpu_session.upgrade_ram(4096);
-				b.map_cap    = _gpu_session.map_buffer(b.id(), true);
+				b.map_cap    = _gpu_session.map_buffer(b.id(), true,
+				                                       Gpu::Mapping_attributes::rw());
 				b.map_offset = static_cast<Offset>(_env.rm().attach(b.map_cap));
 				offset       = b.map_offset;
 

repos/os/include/gpu_session/client.h

@@ -57,8 +57,9 @@ class Gpu::Session_client : public Genode::Rpc_client<Session>
 			call<Rpc_free_buffer>(id); }
 
 		Genode::Dataspace_capability map_buffer(Buffer_id id,
-		                                        bool aperture) override {
+		                                        bool aperture,
-			return call<Rpc_map_buffer>(id, aperture); }
+		                                        Mapping_attributes attrs) override {
+			return call<Rpc_map_buffer>(id, aperture, attrs); }
 
 		void unmap_buffer(Buffer_id id) override {
 			call<Rpc_unmap_buffer>(id); }

repos/os/include/gpu_session/gpu_session.h

@@ -24,6 +24,30 @@ namespace Gpu {
 	struct Buffer;
 	using Buffer_id = Genode::Id_space<Buffer>::Id;
 
+	/*
+	 * Attributes for mapping a buffer
+	 */
+	struct Mapping_attributes
+	{
+		bool readable;
+		bool writeable;
+
+		static Mapping_attributes ro()
+		{
+			return { .readable = true, .writeable = false };
+		}
+
+		static Mapping_attributes rw()
+		{
+			return { .readable = true, .writeable = true };
+		}
+
+		static Mapping_attributes wo()
+		{
+			return { .readable = false, .writeable = true };
+		}
+	};
+
 	struct Sequence_number;
 	struct Session;
 }
@@ -118,11 +142,13 @@ struct Gpu::Session : public Genode::Session
 	 * \param id        buffer id
 	 * \param aperture  if true create CPU accessible mapping through
 	 *                  GGTT window, otherwise create PPGTT mapping
+	 * \param attrs     specify how the buffer is mapped
 	 *
 	 * \throw Mapping_buffer_failed
 	 */
 	virtual Genode::Dataspace_capability map_buffer(Buffer_id id,
-	                                                bool aperture) = 0;
+	                                                bool aperture,
+	                                                Mapping_attributes attrs) = 0;
 
 	/**
 	 * Unmap buffer
@@ -175,7 +201,7 @@ struct Gpu::Session : public Genode::Session
 	GENODE_RPC(Rpc_free_buffer, void, free_buffer, Gpu::Buffer_id);
 	GENODE_RPC_THROW(Rpc_map_buffer, Genode::Dataspace_capability, map_buffer,
 	                 GENODE_TYPE_LIST(Mapping_buffer_failed, Out_of_ram),
-	                 Gpu::Buffer_id, bool);
+	                 Gpu::Buffer_id, bool, Gpu::Mapping_attributes);
 	GENODE_RPC(Rpc_unmap_buffer, void, unmap_buffer,
 	           Gpu::Buffer_id);
 	GENODE_RPC_THROW(Rpc_map_buffer_ppgtt, bool, map_buffer_ppgtt,

repos/os/src/drivers/gpu/intel/main.cc

@@ -1676,8 +1676,13 @@ class Gpu::Session_component : public Genode::Session_object<Gpu::Session>
 		}
 
 		Genode::Dataspace_capability map_buffer(Gpu::Buffer_id id,
-		                                        bool aperture) override
+		                                        bool aperture,
+		                                        Gpu::Mapping_attributes attrs) override
 		{
+			/* treat GGTT mapped buffers as rw */
+			if (!(attrs.readable && attrs.writeable))
+				return Genode::Dataspace_capability();
+
 			Genode::Dataspace_capability map_cap;
 
 			auto lookup_and_map = [&] (Buffer &buffer) {