libdrm works on x86_64!

README.adoc

@@ -388,20 +388,14 @@ flooding the screen with colors. See also: https://superuser.com/questions/22309
 ==== Graphic mode arm
 
 ....
-./run -aa -x -- -vnc :0
+./run -aa -x
 ....
 
-and on another shell:
-
-....
-vinagre :5900
-....
-
-Outcome: you see the penguin, and some boot messages, but don't get a shell.
+Outcome: a window opens, and you see the penguin, and some boot messages there, but don't get a shell there, only on the host terminal.
 
 TODO:
 
-* why is the SDL window not opening, which forces us to use VNC? https://lists.gnu.org/archive/html/qemu-discuss/2018-05/msg00037.html
+* sometimes the SDL window was not opening, a workaround was to use VNC: https://lists.gnu.org/archive/html/qemu-discuss/2018-05/msg00037.html
 * how to get a shell on that graphic window? I don't think `CONFIG_FB_CONSOLE` works since we are not using fbdev but <<drm>>. Maybe try: https://github.com/dvdhrm/kmscon and then obviously: https://github.com/robclark/kmscube
 
 This relies on the QEMU CLI option:
@@ -425,7 +419,7 @@ It is also fun to pass the `-device` multiple times and see that multiple screen
 ./run -aA -x -- -device virtio-gpu-pci
 ....
 
-Multiple `/dev/dri/cardN` are also created accordingly.
+Multiple `/dev/dri/cardN` are also created accordingly. More details at: <<drm>>.
 
 See also https://wiki.qemu.org/Documentation/Platforms/ARM (recently edited and corrected by yours truly... :-)).
 
@@ -3776,59 +3770,48 @@ Looks like a recompile is needed to modify the image...
 
 === DRM
 
-TODO: get something working. Anything. How can an interface be so under-documented and under-exemplified? It boggles my mind.
-
-DRM / DRI is the new interface that supersedes `fbdev`.
-
-We set `CONFIG_DRM=y` on our default kernel configuration, and it creates:
+DRM / DRI is the new interface that supersedes `fbdev`:
 
 ....
-# ls -l /dev/dri
-total 0
-crw-------    1 root     root      226,   0 May 28 09:41 card0
-# grep 226 /proc/devices
-226 drm
-# ls /sys/module/drm /sys/module/drm_kms_helper/
+./build -B 'BR2_PACKAGE_LIBDRM=y' -k
+./run -F '/libdrm_modeset.out' -x
 ....
 
-Some failed attempts: libdrm:
+Source: link:kernel_module/user/libdrm_modeset.c[]
+
+Outcome: for a few seconds, the screen that contains the terminal gets taken over by changing colors of the rainbow.
+
+TODO not working for `aarch64`, it takes over the screen for a few seconds and the kernel messages disappear, but the screen stays black all the time.
 
 ....
-./build -B 'BR2_PACKAGE_LIBDRM=y'
-wget -O kernel_module/user/modeset.c https://raw.githubusercontent.com/dvdhrm/docs/fad7c3203b14e67053e0fc41d8490138b8ff47dd/drm-howto/modeset.c
-./build -k
+./build -B 'BR2_PACKAGE_LIBDRM=y' -k
+./run -F '/libdrm_modeset.out' -x
 ....
 
-fails with:
+We set `CONFIG_DRM=y` on our default kernel configuration, and it creates one device file for each display:
 
 ....
-In file included from modeset.c:40:0:
-/home/ciro/bak/git/linux-kernel-module-cheat/out/x86_64/buildroot/host/x86_64-buildroot-linux-uclibc/sysroot/usr/include/xf86drm.h:40:17: fatal error: drm.h: No such file or directory
- #include <drm.h>
-                 ^
+# ls -l /dev/dri
+total 0
+crw-------    1 root     root      226,   0 May 28 09:41 card0
+# grep 226 /proc/devices
+226 drm
+# ls /sys/module/drm /sys/module/drm_kms_helper/
 ....
 
-Report: https://bugs.busybox.net/show_bug.cgi?id=11056
-
-This file appears to come from the Linux kernel tree:
+Try creating new displays:
 
 ....
-linux/include/uapi/drm/drm.h
+./run -aA -x -- -device virtio-gpu-pci
 ....
 
-e.g. for `drm_context_t`. It does appear under `out/*/build/linux-headers`, but does not show up on `target/`.
-
-libdri2 attempt:
+to see multiple `/dev/dri/cardN`, and then use a different display with:
 
 ....
-./build -B 'BR2_PACKABE_LIBDRI2=y'
-wget -O kernel_module/user/dri2test.c https://raw.githubusercontent.com/robclark/libdri2/master/test/dri2test.c
-./build -k
+./run -F '/libdrm_modeset.out' -x
 ....
 
-but then I noticed that that example requires multiple files, and I don't feel like integrating it into our build. And when I build it on Ubuntu 18.04 host, it does not generate any executable, so I'm confused.
-
-Ubuntu 18.04 host attempts:
+Ubuntu 18.04 host attempts with an NVIDIA graphics cards failed, it seems that NVIDIA takes over:
 
 * https://github.com/dvdhrm/kmscon/issues/113 `driver does not support dumb buffers`
 * https://github.com/Aetf/kmscon/issues/2#issuecomment-392484043 kmscon attempt
@@ -3847,6 +3830,22 @@ Bibliography:
 * https://en.wikipedia.org/wiki/Mode_setting KMS
 * https://github.com/dvdhrm/docs
 
+==== libdri2
+
+TODO get working.
+
+Looks like a more raw alternative to libdrm:
+
+....
+./build -B 'BR2_PACKABE_LIBDRI2=y'
+wget -O kernel_module/user/dri2test.c https://raw.githubusercontent.com/robclark/libdri2/master/test/dri2test.c
+./build -k
+....
+
+but then I noticed that that example requires multiple files, and I don't feel like integrating it into our build.
+
+When I build it on Ubuntu 18.04 host, it does not generate any executable, so I'm confused.
+
 === Linux kernel testing
 
 https://stackoverflow.com/questions/3177338/how-is-the-linux-kernel-tested
@@ -5479,7 +5478,7 @@ Header only linear algebra library supported by Buildroot:
 
 ....
 ./build -B 'BR2_PACKAGE_EIGEN=y' -k
-./run -F '/eigen.out;/eigen_svd.out'
+./run -F '/eigen_hello.out;/eigen_svd.out'
 ....
 
 Source:

kernel_module/external.mk

@@ -8,17 +8,22 @@ KERNEL_MODULE_VERSION = 1.0
 KERNEL_MODULE_SITE = $(BR2_EXTERNAL_KERNEL_MODULE_PATH)
 KERNEL_MODULE_SITE_METHOD = local
 
-ifeq ($(BR2_PACKAGE_OPENBLAS),y)
-	KERNEL_MODULE_DEPENDENCIES += openblas
-endif
 ifeq ($(BR2_PACKAGE_EIGEN),y)
 	KERNEL_MODULE_DEPENDENCIES += eigen
 endif
+ifeq ($(BR2_PACKAGE_LIBDRM),y)
+	KERNEL_MODULE_DEPENDENCIES += libdrm
+endif
+ifeq ($(BR2_PACKAGE_OPENBLAS),y)
+	KERNEL_MODULE_DEPENDENCIES += openblas
+endif
 
 define KERNEL_MODULE_BUILD_CMDS
 	$(MAKE) -C '$(@D)/user' $(TARGET_CONFIGURE_OPTS) \
+	  BR2_PACKAGE_EIGEN="$(BR2_PACKAGE_EIGEN)" \
+	  BR2_PACKAGE_LIBDRM="$(BR2_PACKAGE_LIBDRM)" \
 	  BR2_PACKAGE_OPENBLAS="$(BR2_PACKAGE_OPENBLAS)" \
-	  BR2_PACKAGE_EIGEN="$(BR2_PACKAGE_EIGEN)"
+	;
 endef
 
 define KERNEL_MODULE_INSTALL_TARGET_CMDS

kernel_module/user/Makefile

@@ -7,18 +7,22 @@ LIBS :=
 OUT_EXT ?= .out
 
 OUTS := $(foreach IN_EXT,$(IN_EXT_C) $(IN_EXT_CXX),$(addsuffix $(OUT_EXT), $(basename $(wildcard *$(IN_EXT)))))
+ifeq ($(BR2_PACKAGE_EIGEN),y)
+	CXXFLAGS_EXTRA += $(shell $(PKG_CONFIG) --cflags --libs eigen3)
+else
+	OUTS := $(filter-out eigen_%$(OUT_EXT),$(OUTS))
+endif
+ifeq ($(BR2_PACKAGE_LIBDRM),y)
+	LIBS += $(shell $(PKG_CONFIG) --libs libdrm)
+	CFLAGS_EXTRA += $(shell $(PKG_CONFIG) --cflags libdrm)
+else
+	OUTS := $(filter-out libdrm_%$(OUT_EXT),$(OUTS))
+endif
 ifeq ($(BR2_PACKAGE_OPENBLAS),y)
 	LIBS += -lopenblas
 else
 	OUTS := $(filter-out openblas$(OUT_EXT),$(OUTS))
 endif
-ifeq ($(BR2_PACKAGE_EIGEN),y)
-	# Header only.
-	#LIBS += -leigen
-	CXXFLAGS_EXTRA += $(shell $(PKG_CONFIG) --cflags --libs eigen3)
-else
-	OUTS := $(filter-out eigen%$(OUT_EXT),$(OUTS))
-endif
 
 all: $(OUTS)