At 06:18 PM 6/17/2011, Bernie Thompson wrote:
On Fri, Jun 17, 2011 at 4:10 PM, Steve Strobel <steve.strobel@xxxxxxxxxxxxx> wrote: > It does not have address lines, so the framebuffer memory > is not directly accessible > > If someone could point me to a driver that works in a similar way, it would > help me out a lot. Â Thanks. Hi Steve - there are several drivers that handle this kind of case, including the udlfb driver for DisplayLink USB graphics chips (in the kernel tree /drivers/video/udlfb.c)
That helps a lot. I will check it out. Is there something other than the source code that I should read to get up to speed on it?
The main unsolved challenge is fbdev (in the memory mapped framebuffer case) assumes writes to the framebuffer take effect immediately. [snip]
If I am understanding you right, the challenge is knowing when to flush the changed framebuffer memory to the graphics hardware.
1) Use of /driver/video/fb_defio.c to use the MMU to trigger...
I don't know if a Blackfin system could support that method or not. It doesn't have a full MMU with virtual memory (it runs uClinux), but it does have a memory protection unit. I suppose all that would be needed is to be notified when the framebuffer memory is written to; I think it could do that.
2) Use of an ioctl to allow the user mode client to inform the framebuffer of changed pixels (usually xorg forwarding X DAMAGE notifications, which are well matched for this purpose). This works well and is simple, however we don't yet have a standardized ioctl, so several drivers have different ioctls and thus custom x servers, instead of being supported by the standard xf86-video-fbdev driver.
Since this is a custom embedded system, we are in control of all of the software on it. So we can just make sure that everything included is set up for the same ioctl.
#2 would be the quickest way to give Linux a clean way of handling remote (non-directly-addressable) framebuffers. Others may have some additional suggestions.
Someone suggested to me using the double-buffer flipping logic. Does it get flipped on every screen refresh, or just when the contents of one buffer have been changed?
Hope that helps. Best wishes, Bernie http://plugable.com/
Thanks a bunch, Steve --- Steve Strobel Link Communications, Inc. 1035 Cerise Rd Billings, MT 59101-7378 (406) 245-5002 ext 102 (406) 245-4889 (fax) WWW: http://www.link-comm.com MailTo:steve.strobel@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
