Hi,
Can I control a graphics card _completely_ with DRI? I mean allocate the framebuffer, switch between modes etc. Or do I need some kind of helper code that does these things (like fbdev or the Xserver)? I'm particulary interested in allocating memory for the framebuffer via DRI, I think there is an ioctl for that, but I'm not sure. And is it possible to allocate offscreen memory with DRI? So I could render into it, read the pixels out of it and put them into an image (for example).
I've checked out the cvs drm and mesa tree and did a bit of browsing..
In the mesa tree under src/mesa/drivers/dri/*/xxx_context.c, there usually is xxxMakeCurrent, xxxCreateContext, xxxDestroyContext, but no xxxCreateFramebuffer. It seems that the framebuffer is allocated somewhere else, not in the dri code.
Then I found this nice file in the drm tree: linux-core/drm_drawable.c But it's almost empty, only two noop functions. What are they for? Are they used somewhere? Is DRM_IOCTL_ADD_DRAW used?
It seems to me that the framebuffer is allocated from the main meory, not from the videocard memory.
Ok, I think I've found it: linux-code/drm_bufs.c::drm_addmap (or DRM_IOCTL_ADD_MAP).
typedef struct drm_map {
unsigned long offset; /**< Requested physical address (0 for SAREA)*/
unsigned long size; /**< Requested physical size (bytes) */
drm_map_type_t type; /**< Type of memory to map */
drm_map_flags_t flags; /**< Flags */
void *handle; /**< User-space: "Handle" to pass to mmap() */
/**< Kernel-space: kernel-virtual address */
int mtrr; /**< MTRR slot used */
/* Private data */
} drm_map_t;How can the userspace know which offset is free? Or is it possible to map two overlapping areas? In drm_bufs.c::drm_addmap is:
case _DRM_AGP:
if (drm_core_has_AGP(dev)) {
map->offset += dev->agp->base;
map->mtrr = dev->agp->agp_mtrr; /* for getmap */
}
It just returns the offset plus the start of the agp memory, but no checks for overlapping maps, so is it possible to do the following?
drm_addmap(type = _DRM_AGP, offset = 0, size = 100)
drm_addmap(type = _DRM_AGP, offset = 10, size = 90)
Does the agp memory have some size restrictions? Or can I map any size? drm_addmap(type = _DRM_AGP, offset = 0, size = MAX_INT)?
thanks tom
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