path: root/fb.c

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <pthread.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <inttypes.h>
#include <xf86drm.h>
#include <xf86drmMode.h>
#include <stddef.h>
#include <stdint.h>
#include <sys/ioctl.h>
#include <sys/mman.h>

#include "fb.h"
#include "util.h"

/* Copyright (C) 2016 Vito Caputo <vcaputo@pengaru.com> */


/* I've used a separate thread for page-flipping duties because the libdrm api
 * (and related kernel ioctl) for page flips doesn't appear to support queueing
 * multiple flip requests.  In this use case we aren't interactive and wish to
 * just accumulate rendered pages until we run out of spare pages, allowing the
 * renderer to get as far ahead of vsync as possible, and certainly never
 * blocked waiting for vsync unless there's no spare page available for drawing
 * into.
 *
 * In lieu of a queueing mechanism on the drm fd, we must submit the next page
 * once the currently submitted page is flipped to - it's at that moment we
 * won't get EBUSY from the ioctl any longer.  Without a dedicated thread
 * submitting flip requests and synchronously consuming their flip events,
 * we're liable to introduce latency in the page flip submission if implemented
 * in a more opportunistic manner whenever the fb api is entered from the
 * render loop.
 *
 * If the kernel simply let us queue multiple flip requests we could maintain
 * our submission queue entirely in the drm fd, and get available pages from
 * the drm event handler once our pool of pages is depleted.  The kernel on
 * vsync could check the fd to see if another flip is queued and there would be
 * the least latency possible in submitting the flips - the least likely to
 * miss a vsync.  This would also elide the need for synchronization in
 * userspace between the renderer and the flipper thread, since there would no
 * longer be a flipper thread.
 *
 * Let me know if you're aware of a better way with existing mainline drm!
 */


/* Most of fb_page_t is kept private, the public part is
 * just an fb_fragment_t describing the whole page.
 */
typedef struct _fb_page_t _fb_page_t;
struct _fb_page_t {
	_fb_page_t	*next;
	uint32_t	*mmap;
	size_t		mmap_size;
	uint32_t	drm_dumb_handle;
	uint32_t	drm_fb_id;
	fb_page_t	public_page;
};

typedef struct fb_t {
	pthread_t	thread;
	int		drm_fd;
	uint32_t	drm_crtc_id;

	_fb_page_t	*active_page;		/* page currently displayed */

	pthread_mutex_t	ready_mutex;
	pthread_cond_t	ready_cond;
	_fb_page_t	*ready_pages_head;	/* next pages to flip to */
	_fb_page_t	*ready_pages_tail;

	pthread_mutex_t	inactive_mutex;
	pthread_cond_t	inactive_cond;
	_fb_page_t	*inactive_pages;	/* finished pages available for (re)use */

	unsigned	put_pages_count;
} fb_t;

#ifndef container_of
#define container_of(_ptr, _type, _member) \
	(_type *)((void *)(_ptr) - offsetof(_type, _member))
#endif


/* Synchronize with the page flip by waiting for its event. */
static inline void fb_drm_flip_wait(fb_t *fb)
{
	drmEventContext	drm_ev_ctx = {
				.version = DRM_EVENT_CONTEXT_VERSION,
				.vblank_handler = NULL,
				.page_flip_handler = NULL
			};
	drmHandleEvent(fb->drm_fd, &drm_ev_ctx);
}


/* Consumes ready pages queued via fb_page_put(), submits them to drm to flip
 * on vsync.  Produces inactive pages from those replaced, making them
 * available to fb_page_get(). */
static void * fb_flipper_thread(void *_fb)
{
	fb_t	*fb = _fb;

	for (;;) {
		_fb_page_t	*next_active_page;
		/* wait for a flip req, submit the req page for flip on vsync, wait for it to flip before making the
		 * active page inactive/available, repeat.
		 */
		pthread_mutex_lock(&fb->ready_mutex);
		while (!fb->ready_pages_head)
			pthread_cond_wait(&fb->ready_cond, &fb->ready_mutex);

		next_active_page = fb->ready_pages_head;
		fb->ready_pages_head = next_active_page->next;
		if (!fb->ready_pages_head)
			fb->ready_pages_tail = NULL;
		pthread_mutex_unlock(&fb->ready_mutex);

		/* submit the next active page for page flip on vsync, and wait for it. */
		pexit_if(drmModePageFlip(fb->drm_fd, fb->drm_crtc_id, next_active_page->drm_fb_id, DRM_MODE_PAGE_FLIP_EVENT, NULL) < 0,
			"unable to flip page");
		fb_drm_flip_wait(fb);

		/* now that we're displaying a new page, make the previously active one inactive so rendering can reuse it */
		pthread_mutex_lock(&fb->inactive_mutex);
		fb->active_page->next = fb->inactive_pages;
		fb->inactive_pages = fb->active_page;
		pthread_cond_signal(&fb->inactive_cond);
		pthread_mutex_unlock(&fb->inactive_mutex);

		fb->active_page = next_active_page;
	}
}


/* creates a framebuffer page, which is a coupled drm_fb object and mmap region of memory */
static void fb_page_new(fb_t *fb, drmModeModeInfoPtr mode)
{
	_fb_page_t			*page;
	struct drm_mode_create_dumb	create_dumb = {
						.width = mode->hdisplay,
						.height = mode->vdisplay,
						.bpp = 32,
						.flags = 0, // unused,
					};
	struct drm_mode_map_dumb	map_dumb = {
						.pad = 0, // unused
					};
	uint32_t			*map, fb_id;

	page = calloc(1, sizeof(_fb_page_t));

	pexit_if(ioctl(fb->drm_fd, DRM_IOCTL_MODE_CREATE_DUMB, &create_dumb) < 0,
		"unable to create dumb buffer");

	map_dumb.handle = create_dumb.handle;
	pexit_if(ioctl(fb->drm_fd, DRM_IOCTL_MODE_MAP_DUMB, &map_dumb) < 0,
		"unable to prepare dumb buffer for mmap");
	pexit_if(!(map = mmap(NULL, create_dumb.size, PROT_READ|PROT_WRITE, MAP_SHARED, fb->drm_fd, map_dumb.offset)),
		"unable to mmap dumb buffer");
	pexit_if(drmModeAddFB(fb->drm_fd, mode->hdisplay, mode->vdisplay, 24, 32, create_dumb.pitch, create_dumb.handle, &fb_id) < 0,
		"unable to add dumb buffer");

	page->mmap = map;
	page->mmap_size = create_dumb.size;
	page->drm_dumb_handle = map_dumb.handle;
	page->drm_fb_id = fb_id;

	page->public_page.fragment.buf = map;
	page->public_page.fragment.width = mode->hdisplay;
	page->public_page.fragment.height = mode->vdisplay;
	page->public_page.fragment.stride = create_dumb.pitch - (mode->hdisplay * 4);

	page->next = fb->inactive_pages;
	fb->inactive_pages = page;
}


static void _fb_page_free(fb_t *fb, _fb_page_t *page)
{
	struct drm_mode_destroy_dumb	destroy_dumb = {
						.handle = page->drm_dumb_handle,
					};

	drmModeRmFB(fb->drm_fd, page->drm_fb_id);
	munmap(page->mmap, page->mmap_size);
	ioctl(fb->drm_fd, DRM_IOCTL_MODE_DESTROY_DUMB, &destroy_dumb); // XXX: errors?
	free(page);
}


/* get the next inactive page from the fb, waiting if necessary. */
static inline _fb_page_t * _fb_page_get(fb_t *fb)
{
	_fb_page_t	*page;

	/* As long as n_pages is >= 3 this won't block unless we're submitting
	 * pages faster than vhz.
	 */
	pthread_mutex_lock(&fb->inactive_mutex);
	while (!(page = fb->inactive_pages))
		pthread_cond_wait(&fb->inactive_cond, &fb->inactive_mutex);
	fb->inactive_pages = page->next;
	pthread_mutex_unlock(&fb->inactive_mutex);

	page->next = NULL;

	return page;
}


/* public interface */
fb_page_t * fb_page_get(fb_t *fb)
{
	return &(_fb_page_get(fb)->public_page);
}


/* put a page into the fb, queueing for display */
static inline void _fb_page_put(fb_t *fb, _fb_page_t *page)
{
	pthread_mutex_lock(&fb->ready_mutex);
	if (fb->ready_pages_tail)
		fb->ready_pages_tail->next = page;
	else
		fb->ready_pages_head = page;

	fb->ready_pages_tail = page;
	pthread_cond_signal(&fb->ready_cond);
	pthread_mutex_unlock(&fb->ready_mutex);
}


/* public interface */

/* put a page into the fb, queueing for display */
void fb_page_put(fb_t *fb, fb_page_t *page)
{
	fb->put_pages_count++;

	_fb_page_put(fb, container_of(page, _fb_page_t, public_page));
}


/* get (and reset) the current count of put pages */
void fb_get_put_pages_count(fb_t *fb, unsigned *count)
{
	*count = fb->put_pages_count;
	fb->put_pages_count = 0;
}


/* free the fb and associated resources */
void fb_free(fb_t *fb)
{
	if (fb->active_page) {
		pthread_cancel(fb->thread);
		pthread_join(fb->thread, NULL);
	}

	/* TODO: free all the pages */

	pthread_mutex_destroy(&fb->ready_mutex);
	pthread_cond_destroy(&fb->ready_cond);
	pthread_mutex_destroy(&fb->inactive_mutex);
	pthread_cond_destroy(&fb->inactive_cond);

	free(fb);
}


/* create a new fb instance */
fb_t * fb_new(int drm_fd, uint32_t crtc_id, uint32_t *connectors, int n_connectors, drmModeModeInfoPtr mode, int n_pages)
{
	int		i;
	_fb_page_t	*page;
	fb_t		*fb;

	fb = calloc(1, sizeof(fb_t));
	if (!fb)
		return NULL;

	fb->drm_fd = drm_fd;
	fb->drm_crtc_id = crtc_id;

	for (i = 0; i < n_pages; i++)
		fb_page_new(fb, mode);

	pthread_mutex_init(&fb->ready_mutex, NULL);
	pthread_cond_init(&fb->ready_cond, NULL);
	pthread_mutex_init(&fb->inactive_mutex, NULL);
	pthread_cond_init(&fb->inactive_cond, NULL);

	page = _fb_page_get(fb);

	/* set the video mode, pinning this page, set it as the active page. */
	if (drmModeSetCrtc(drm_fd, crtc_id, page->drm_fb_id, 0, 0, connectors, n_connectors, mode) < 0) {
		_fb_page_free(fb, page);
		fb_free(fb);
		return NULL;
	}

	fb->active_page = page;

	/* start up the page flipper thread */
	pthread_create(&fb->thread, NULL, fb_flipper_thread, fb);

	return fb;
}


/* divide a fragment into n_fragments, storing their values into fragments[],
 * which is expected to have n_fragments of space. */
void fb_fragment_divide(fb_fragment_t *fragment, unsigned n_fragments, fb_fragment_t fragments[])
{
	unsigned	slice = fragment->height / n_fragments;
	unsigned	i;
	void		*buf = fragment->buf;
	unsigned	pitch = (fragment->width * 4) + fragment->stride;
	unsigned	y = fragment->y;

	/* This just splits the supplied fragment into even horizontal slices */
	/* TODO: It probably makes sense to add an fb_fragment_tile() as well, since some rendering
	 * algorithms benefit from the locality of a tiled fragment.
	 */

	for (i = 0; i < n_fragments; i++) {
		fragments[i].buf = buf;
		fragments[i].x = fragment->x;
		fragments[i].y = y;
		fragments[i].width = fragment->width;
		fragments[i].height = slice;
		fragments[i].stride = fragment->stride;

		buf += pitch * slice;
		y += slice;
	}
	/* TODO: handle potential fractional tail slice? */
}