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The following commit(s) were added to refs/heads/master by this push:
new 249df8c1d9f video/fb: guarantee fb read-write integrity to prevent
display tearing
249df8c1d9f is described below
commit 249df8c1d9f4942b7105344ccd01d051bd7b3957
Author: zhanxiaoqi <[email protected]>
AuthorDate: Wed Apr 15 10:54:52 2026 +0800
video/fb: guarantee fb read-write integrity to prevent display tearing
Serialization has been added to the paths of fb_read/fb_write, as well as
partial reading of plane/video information, updatearea, pandisplay, etc.
This covers the scenario where "one thread draws/switches via the character
device interface while another thread reads the framebuffer via the
character device interface", ensuring that the read framebuffer data
is complete and preventing screen tearing.
Signed-off-by: zhanxiaoqi <[email protected]>
---
drivers/video/fb.c | 45 +++++++++++++++++++++++++++++++++++++++++----
1 file changed, 41 insertions(+), 4 deletions(-)
diff --git a/drivers/video/fb.c b/drivers/video/fb.c
index 1f7e15d6e8d..881a7b1d94d 100644
--- a/drivers/video/fb.c
+++ b/drivers/video/fb.c
@@ -47,6 +47,7 @@
#include <nuttx/circbuf.h>
#include <nuttx/sched_note.h>
+#include <nuttx/mutex.h>
#ifdef CONFIG_VIDEO_FB_SPLASHSCREEN
# include <nuttx/signal.h>
#endif
@@ -115,8 +116,9 @@ struct fb_chardev_s
uint8_t plane; /* Video plan number */
clock_t vsyncoffset; /* VSync offset ticks */
FAR struct fb_priv_s *head;
- FAR struct fb_paninfo_s *paninfo; /* Pan info array */
- size_t paninfo_count; /* Pan info count */
+ FAR struct fb_paninfo_s *paninfo; /* Pan info array */
+ size_t paninfo_count; /* Pan info count */
+ mutex_t lock; /* Framebuffer device lock */
};
struct fb_panelinfo_s
@@ -248,7 +250,9 @@ static int fb_splashscreen(FAR struct fb_videoinfo_s *vinfo,
FAR uint8_t *dst;
unsigned int row;
unsigned int nrun;
+ unsigned int width;
FAR fb_pixel_t *buf;
+ FAR fb_pixel_t *bufp;
FAR fb_pixel_t colour;
int ret = OK;
@@ -293,8 +297,7 @@ static int fb_splashscreen(FAR struct fb_videoinfo_s *vinfo,
for (row = 0; row < g_splscr.height; row++)
{
- unsigned int width;
- FAR fb_pixel_t *bufp = buf; /* Start address of the buffer */
+ bufp = buf; /* Start address of the buffer */
/* Process each run-length encoded pixel in the image */
@@ -563,10 +566,12 @@ static ssize_t fb_read(FAR struct file *filep, FAR char
*buffer, size_t len)
/* Get panel info */
+ nxmutex_lock(&fb->lock);
ret = fb_get_panelinfo(fb, &panelinfo, priv->overlay);
if (ret < 0)
{
+ nxmutex_unlock(&fb->lock);
return ret;
}
@@ -575,6 +580,7 @@ static ssize_t fb_read(FAR struct file *filep, FAR char
*buffer, size_t len)
start = filep->f_pos;
if (start >= panelinfo.fblen)
{
+ nxmutex_unlock(&fb->lock);
return 0; /* Return end-of-file */
}
@@ -590,6 +596,7 @@ static ssize_t fb_read(FAR struct file *filep, FAR char
*buffer, size_t len)
memcpy(buffer, panelinfo.fbmem + start, size);
filep->f_pos += size;
+ nxmutex_unlock(&fb->lock);
return size;
}
@@ -621,10 +628,12 @@ static ssize_t fb_write(FAR struct file *filep, FAR const
char *buffer,
/* Get panel info */
+ nxmutex_lock(&fb->lock);
ret = fb_get_panelinfo(fb, &panelinfo, priv->overlay);
if (ret < 0)
{
+ nxmutex_unlock(&fb->lock);
return ret;
}
@@ -633,6 +642,7 @@ static ssize_t fb_write(FAR struct file *filep, FAR const
char *buffer,
start = filep->f_pos;
if (start >= panelinfo.fblen)
{
+ nxmutex_unlock(&fb->lock);
return -EFBIG; /* Cannot extend the framebuffer */
}
@@ -648,6 +658,7 @@ static ssize_t fb_write(FAR struct file *filep, FAR const
char *buffer,
memcpy(panelinfo.fbmem + start, buffer, size);
filep->f_pos += size;
+ nxmutex_unlock(&fb->lock);
return size;
}
@@ -775,7 +786,9 @@ static int fb_ioctl(FAR struct file *filep, int cmd,
unsigned long arg)
break;
}
+ nxmutex_lock(&fb->lock);
ret = fb->vtable->getvideoinfo(fb->vtable, vinfo);
+ nxmutex_unlock(&fb->lock);
}
break;
@@ -785,7 +798,9 @@ static int fb_ioctl(FAR struct file *filep, int cmd,
unsigned long arg)
(FAR struct fb_planeinfo_s *)((uintptr_t)arg);
DEBUGASSERT(pinfo != NULL);
+ nxmutex_lock(&fb->lock);
ret = fb_get_planeinfo(fb, pinfo, pinfo->display);
+ nxmutex_unlock(&fb->lock);
}
break;
@@ -867,7 +882,9 @@ static int fb_ioctl(FAR struct file *filep, int cmd,
unsigned long arg)
break;
}
+ nxmutex_lock(&fb->lock);
ret = fb->vtable->updatearea(fb->vtable, area);
+ nxmutex_unlock(&fb->lock);
}
break;
#endif
@@ -1144,16 +1161,19 @@ static int fb_ioctl(FAR struct file *filep, int cmd,
unsigned long arg)
memcpy(&paninfo, pinfo, sizeof(*pinfo));
+ nxmutex_lock(&fb->lock);
if (fb->vtable->pandisplay != NULL)
{
ret = fb->vtable->pandisplay(fb->vtable, pinfo);
if (ret < 0)
{
+ nxmutex_unlock(&fb->lock);
break;
}
}
ret = fb_add_paninfo(fb, &paninfo, FB_NO_OVERLAY);
+ nxmutex_unlock(&fb->lock);
}
break;
@@ -1183,15 +1203,18 @@ static int fb_ioctl(FAR struct file *filep, int cmd,
unsigned long arg)
break;
}
+ nxmutex_lock(&fb->lock);
ret = fb->vtable->getvideoinfo(fb->vtable, &vinfo);
if (ret < 0)
{
+ nxmutex_unlock(&fb->lock);
break;
}
ret = fb_get_planeinfo(fb, &pinfo, 0);
if (ret < 0)
{
+ nxmutex_unlock(&fb->lock);
break;
}
@@ -1263,6 +1286,8 @@ static int fb_ioctl(FAR struct file *filep, int cmd,
unsigned long arg)
varinfo->transp.length = 8;
break;
}
+
+ nxmutex_unlock(&fb->lock);
}
break;
@@ -1280,15 +1305,18 @@ static int fb_ioctl(FAR struct file *filep, int cmd,
unsigned long arg)
break;
}
+ nxmutex_lock(&fb->lock);
ret = fb->vtable->getvideoinfo(fb->vtable, &vinfo);
if (ret < 0)
{
+ nxmutex_unlock(&fb->lock);
break;
}
ret = fb_get_planeinfo(fb, &pinfo, 0);
if (ret < 0)
{
+ nxmutex_unlock(&fb->lock);
break;
}
@@ -1305,12 +1333,15 @@ static int fb_ioctl(FAR struct file *filep, int cmd,
unsigned long arg)
fixinfo->visual = FB_ISMONO(vinfo.fmt) ?
FB_VISUAL_MONO10 : FB_VISUAL_TRUECOLOR;
fixinfo->line_length = pinfo.stride;
+ nxmutex_unlock(&fb->lock);
}
break;
case FBIOGET_PANINFOCNT:
{
+ nxmutex_lock(&fb->lock);
ret = fb_paninfo_count(fb->vtable, (int)arg);
+ nxmutex_unlock(&fb->lock);
}
break;
@@ -1364,10 +1395,12 @@ static int fb_mmap(FAR struct file *filep, FAR struct
mm_map_entry_s *map)
/* Get panel info */
+ nxmutex_lock(&fb->lock);
ret = fb_get_panelinfo(fb, &panelinfo, priv->overlay);
if (ret < 0)
{
+ nxmutex_unlock(&fb->lock);
return ret;
}
@@ -1385,9 +1418,11 @@ static int fb_mmap(FAR struct file *filep, FAR struct
mm_map_entry_s *map)
#else
map->vaddr = (FAR char *)panelinfo.fbmem + map->offset;
#endif
+ nxmutex_unlock(&fb->lock);
return OK;
}
+ nxmutex_unlock(&fb->lock);
return -EINVAL;
}
@@ -1918,6 +1953,7 @@ int fb_register_device(int display, int plane,
DEBUGASSERT(vtable != NULL);
fb->plane = plane;
fb->vtable = vtable;
+ nxmutex_init(&fb->lock);
/* Initialize the frame buffer instance. */
@@ -2030,6 +2066,7 @@ errout_with_paninfo:
kmm_free(fb->paninfo);
errout_with_fb:
+ nxmutex_destroy(&fb->lock);
kmm_free(fb);
return ret;
}
