drm/vkms: Introduce basic VKMS driver

This patch introduces Virtual Kernel Mode-Setting (VKMS) driver. It
creates a very basic kms driver with 1 crtc/encoder/connector/plane.

VKMS driver would be useful for testing, or for running X (or similar)
on headless machines and be able to still use the GPU. Thus it enables
a virtual display without the need for hardware display capability.

Signed-off-by: Haneen Mohammed <hamohammed.sa@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180514143346.GA21695@haneen-vb

drivers/gpu/drm/Kconfig

@@ -213,6 +213,12 @@ config DRM_VGEM
 	  as used by Mesa's software renderer for enhanced performance.
 	  If M is selected the module will be called vgem.
 
+config DRM_VKMS
+	tristate "Virtual KMS"
+	depends on DRM
+	help
+	  Choose this option to get a virtual kernal mode-setting driver.
+	  If M is selected the module will be called vkms.
 
 source "drivers/gpu/drm/exynos/Kconfig"
 

drivers/gpu/drm/Makefile

@@ -69,6 +69,7 @@ obj-$(CONFIG_DRM_SAVAGE)+= savage/
 obj-$(CONFIG_DRM_VMWGFX)+= vmwgfx/
 obj-$(CONFIG_DRM_VIA)	+=via/
 obj-$(CONFIG_DRM_VGEM)	+= vgem/
+obj-$(CONFIG_DRM_VKMS)	+= vkms/
 obj-$(CONFIG_DRM_NOUVEAU) +=nouveau/
 obj-$(CONFIG_DRM_EXYNOS) +=exynos/
 obj-$(CONFIG_DRM_ROCKCHIP) +=rockchip/

drivers/gpu/drm/vkms/Makefile

@@ -0,0 +1,3 @@
+vkms-y := vkms_drv.o
+
+obj-$(CONFIG_DRM_VKMS) += vkms.o

drivers/gpu/drm/vkms/vkms_drv.c

@@ -0,0 +1,146 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <linux/module.h>
+#include <drm/drmP.h>
+#include <drm/drm_gem.h>
+#include <drm/drm_crtc_helper.h>
+#include "vkms_drv.h"
+
+#define DRIVER_NAME	"vkms"
+#define DRIVER_DESC	"Virtual Kernel Mode Setting"
+#define DRIVER_DATE	"20180514"
+#define DRIVER_MAJOR	1
+#define DRIVER_MINOR	0
+
+static struct vkms_device *vkms_device;
+
+static const struct file_operations vkms_driver_fops = {
+	.owner		= THIS_MODULE,
+	.open		= drm_open,
+	.mmap		= drm_gem_mmap,
+	.unlocked_ioctl	= drm_ioctl,
+	.compat_ioctl	= drm_compat_ioctl,
+	.poll		= drm_poll,
+	.read		= drm_read,
+	.llseek		= no_llseek,
+	.release	= drm_release,
+};
+
+static void vkms_release(struct drm_device *dev)
+{
+	struct vkms_device *vkms = container_of(dev, struct vkms_device, drm);
+
+	platform_device_unregister(vkms->platform);
+	drm_mode_config_cleanup(&vkms->drm);
+	drm_dev_fini(&vkms->drm);
+}
+
+struct drm_driver vkms_driver = {
+	.driver_features	= DRIVER_MODESET | DRIVER_ATOMIC | DRIVER_GEM,
+	.release		= vkms_release,
+	.fops			= &vkms_driver_fops,
+
+	.name			= DRIVER_NAME,
+	.desc			= DRIVER_DESC,
+	.date			= DRIVER_DATE,
+	.major			= DRIVER_MAJOR,
+	.minor			= DRIVER_MINOR,
+};
+
+static const u32 vkms_formats[] = {
+	DRM_FORMAT_XRGB8888,
+};
+
+static void vkms_connector_destroy(struct drm_connector *connector)
+{
+	drm_connector_unregister(connector);
+	drm_connector_cleanup(connector);
+}
+
+static const struct drm_connector_funcs vkms_connector_funcs = {
+	.fill_modes = drm_helper_probe_single_connector_modes,
+	.destroy = vkms_connector_destroy,
+};
+
+static int __init vkms_init(void)
+{
+	int ret;
+
+	vkms_device = kzalloc(sizeof(*vkms_device), GFP_KERNEL);
+	if (!vkms_device)
+		return -ENOMEM;
+
+	ret = drm_dev_init(&vkms_device->drm, &vkms_driver, NULL);
+	if (ret)
+		goto out_free;
+
+	vkms_device->platform =
+		platform_device_register_simple(DRIVER_NAME, -1, NULL, 0);
+	if (IS_ERR(vkms_device->platform)) {
+		ret = PTR_ERR(vkms_device->platform);
+		goto out_fini;
+	}
+
+	drm_mode_config_init(&vkms_device->drm);
+
+	ret = drm_connector_init(&vkms_device->drm, &vkms_device->connector,
+				 &vkms_connector_funcs,
+				 DRM_MODE_CONNECTOR_VIRTUAL);
+	if (ret < 0) {
+		DRM_ERROR("Failed to init connector\n");
+		goto out_unregister;
+	}
+
+	ret = drm_simple_display_pipe_init(&vkms_device->drm,
+					   &vkms_device->pipe,
+					   NULL,
+					   vkms_formats,
+					   ARRAY_SIZE(vkms_formats),
+					   NULL,
+					   &vkms_device->connector);
+	if (ret < 0) {
+		DRM_ERROR("Cannot setup simple display pipe\n");
+		goto out_unregister;
+	}
+
+	ret = drm_dev_register(&vkms_device->drm, 0);
+	if (ret)
+		goto out_unregister;
+
+	drm_connector_register(&vkms_device->connector);
+
+	return 0;
+
+out_unregister:
+	platform_device_unregister(vkms_device->platform);
+out_fini:
+	drm_dev_fini(&vkms_device->drm);
+out_free:
+	kfree(vkms_device);
+
+	return ret;
+}
+
+static void __exit vkms_exit(void)
+{
+	if (!vkms_device) {
+		DRM_INFO("vkms_device is NULL.\n");
+		return;
+	}
+
+	drm_dev_unregister(&vkms_device->drm);
+	drm_dev_put(&vkms_device->drm);
+
+	kfree(vkms_device);
+}
+
+module_init(vkms_init);
+module_exit(vkms_exit);
+
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");

drivers/gpu/drm/vkms/vkms_drv.h

@@ -0,0 +1,13 @@
+#ifndef _VKMS_DRV_H_
+#define _VKMS_DRV_H_
+
+#include <drm/drm_simple_kms_helper.h>
+
+struct vkms_device {
+	struct drm_device drm;
+	struct platform_device *platform;
+	struct drm_simple_display_pipe pipe;
+	struct drm_connector connector;
+};
+
+#endif /* _VKMS_DRV_H_ */