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@xxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxx>
> ---
> 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
>
>
> _______________________________________________
> Linaro-mm-sig mailing list
> Linaro-mm-sig@xxxxxxxxxxxxxxxx
> http://lists.linaro.org/mailman/listinfo/linaro-mm-sig
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