Laurent,
Your recent documentation efforts are extremely commendable. Just a couple of small nits below...
On Wed, Jun 20, 2012 at 7:09 AM, Laurent Pinchart laurent.pinchart@ideasonboard.com wrote:
Add support for the dma-buf exporter role to the frame buffer API. The importer role isn't meaningful for frame buffer devices, as the frame buffer device model doesn't allow using externally allocated memory.
Signed-off-by: Laurent Pinchart laurent.pinchart@ideasonboard.com
Documentation/fb/api.txt | 36 ++++++++++++++++++++++++++++++++++++ drivers/video/fbmem.c | 36 ++++++++++++++++++++++++++++++++++++ include/linux/fb.h | 12 ++++++++++++ 3 files changed, 84 insertions(+), 0 deletions(-)
diff --git a/Documentation/fb/api.txt b/Documentation/fb/api.txt index d4ff7de..f0b2173 100644 --- a/Documentation/fb/api.txt +++ b/Documentation/fb/api.txt @@ -304,3 +304,39 @@ extensions. Upon successful format configuration, drivers update the fb_fix_screeninfo type, visual and line_length fields depending on the selected format. The type and visual fields are set to FB_TYPE_FOURCC and FB_VISUAL_FOURCC respectively.
+5. DMA buffer sharing +---------------------
+The dma-buf kernel framework allows DMA buffers to be shared across devices +and applications. Sharing buffers across display devices and video capture or +video decoding devices allow zero-copy operation when displaying video content +produced by a hardware device such as a camera or a hardware codec. This is +crucial to achieve optimal system performances during video display.
+While dma-buf supports both exporting internally allocated memory as a dma-buf +object (known as the exporter role) and importing a dma-buf object to be used +as device memory (known as the importer role), the frame buffer API only +supports the exporter role, as the frame buffer device model doesn't support +using externally-allocated memory.
+The export a frame buffer as a dma-buf file descriptors, applications call the
s/The/To s/descriptors/descriptor
cheers, Jesse
+FBIOGET_DMABUF ioctl. The ioctl takes a pointer to a fb_dmabuf_export +structure.
+struct fb_dmabuf_export {
- __u32 fd;
- __u32 flags;
+};
+The flag field specifies the flags to be used when creating the dma-buf file +descriptor. The only supported flag is O_CLOEXEC. If the call is successful, +the driver will set the fd field to a file descriptor corresponding to the +dma-buf object.
+Applications can then pass the file descriptors to another application or +another device driver. The dma-buf object is automatically reference-counted, +applications can and should close the file descriptor as soon as they don't +need it anymore. The underlying dma-buf object will not be freed before the +last device that uses the dma-buf object releases it. diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c index 0dff12a..400e449 100644 --- a/drivers/video/fbmem.c +++ b/drivers/video/fbmem.c @@ -15,6 +15,7 @@
#include <linux/compat.h> #include <linux/types.h> +#include <linux/dma-buf.h> #include <linux/errno.h> #include <linux/kernel.h> #include <linux/major.h> @@ -1074,6 +1075,23 @@ fb_blank(struct fb_info *info, int blank) return ret; }
+#ifdef CONFIG_DMA_SHARED_BUFFER +int +fb_get_dmabuf(struct fb_info *info, int flags) +{
- struct dma_buf *dmabuf;
- if (info->fbops->fb_dmabuf_export == NULL)
- return -ENOTTY;
- dmabuf = info->fbops->fb_dmabuf_export(info);
- if (IS_ERR(dmabuf))
- return PTR_ERR(dmabuf);
- return dma_buf_fd(dmabuf, flags);
+} +#endif
static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg) { @@ -1084,6 +1102,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, struct fb_cmap cmap_from; struct fb_cmap_user cmap; struct fb_event event;
- struct fb_dmabuf_export dmaexp;
void __user *argp = (void __user *)arg; long ret = 0;
@@ -1191,6 +1210,23 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, console_unlock(); unlock_fb_info(info); break; +#ifdef CONFIG_DMA_SHARED_BUFFER
- case FBIOGET_DMABUF:
- if (copy_from_user(&dmaexp, argp, sizeof(dmaexp)))
- return -EFAULT;
- if (!lock_fb_info(info))
- return -ENODEV;
- dmaexp.fd = fb_get_dmabuf(info, dmaexp.flags);
- unlock_fb_info(info);
- if (dmaexp.fd < 0)
- return dmaexp.fd;
- ret = copy_to_user(argp, &dmaexp, sizeof(dmaexp))
- ? -EFAULT : 0;
- break;
+#endif default: if (!lock_fb_info(info)) return -ENODEV; diff --git a/include/linux/fb.h b/include/linux/fb.h index ac3f1c6..c9fee75 100644 --- a/include/linux/fb.h +++ b/include/linux/fb.h @@ -39,6 +39,7 @@ #define FBIOPUT_MODEINFO 0x4617 #define FBIOGET_DISPINFO 0x4618 #define FBIO_WAITFORVSYNC _IOW('F', 0x20, __u32) +#define FBIOGET_DMABUF _IOR('F', 0x21, struct fb_dmabuf_export)
#define FB_TYPE_PACKED_PIXELS 0 /* Packed Pixels */ #define FB_TYPE_PLANES 1 /* Non interleaved planes */ @@ -403,6 +404,11 @@ struct fb_cursor { #define FB_BACKLIGHT_MAX 0xFF #endif
+struct fb_dmabuf_export {
- __u32 fd;
- __u32 flags;
+};
#ifdef __KERNEL__
#include <linux/fs.h> @@ -418,6 +424,7 @@ struct vm_area_struct; struct fb_info; struct device; struct file; +struct dma_buf;
/* Definitions below are used in the parsed monitor specs */ #define FB_DPMS_ACTIVE_OFF 1 @@ -701,6 +708,11 @@ struct fb_ops { /* called at KDB enter and leave time to prepare the console */ int (*fb_debug_enter)(struct fb_info *info); int (*fb_debug_leave)(struct fb_info *info);
+#ifdef CONFIG_DMA_SHARED_BUFFER
- /* Export the frame buffer as a dmabuf object */
- struct dma_buf *(*fb_dmabuf_export)(struct fb_info *info);
+#endif };
#ifdef CONFIG_FB_TILEBLITTING
Regards,
Laurent Pinchart
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