linux-kernel - Re: Dynamically attaching fbcon to a framebuffer

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Message-ID: <37885b84bd22291f359459562a674222.squirrel@intranet.cs.nmsu.edu>
Date:	Wed, 2 Dec 2009 10:06:41 -0700
From:	"Rick L. Vinyard, Jr." <rvinyard@...nmsu.edu>
To:	"Alan Cox" <alan@...rguk.ukuu.org.uk>
Cc:	"Greg KH" <greg@...ah.com>,
	"Linux USB" <linux-usb@...r.kernel.org>,
	"LKML" <linux-kernel@...r.kernel.org>
Subject: Re: Dynamically attaching fbcon to a framebuffer

Alan Cox wrote:
>> I have the display as a framebuffer device now (based on fbdefio with
>> the
>> hid device as the parent).
>>
>> Do I really need a separate console device or can I just use fbcon?
>
> fbcon should do what you want.
>

I've been playing with fbcon, but can't get a fbcon console started.

I wrote a little app that uses the framebuffer ioctls to change fbcon's
map. Specifically, the G13 shows up as fb1, and the app basically does
this:

  int fd = open("/dev/fb1", O_RDWR);
  struct fb_con2fbmap con2fb;
  int ret;

  if ( fd < 0 ) { printf("Error opening %s\n", DEVICE); return -1; }

  con2fb.console = 5;

  ioctl(fd, FBIOGET_CON2FBMAP, &con2fb);
  printf("Console: %d  Framebuffer: %d\n", con2fb.console,
con2fb.framebuffer);

  con2fb.framebuffer = 1;
  ret = ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb);
  printf("Succeeded: %d\n", ret);

  ioctl(fd, FBIOGET_CON2FBMAP, &con2fb);
  printf("Console: %d  Framebuffer: %d\n", con2fb.console,
con2fb.framebuffer);

This succeeds and I get:
Console: 5  Framebuffer: 0
Succeeded: 0
Console: 5  Framebuffer: 1

But, when I change to console 5 that's when things die. I never hit any of
my fb_ops callbacks.

The driver can be found here:
http://g13.svn.sourceforge.net/viewvc/g13/driver/trunk/hid-g13.h
http://g13.svn.sourceforge.net/viewvc/g13/driver/trunk/hid-g13.c

This doesn't actually do anything but do a printk (in hex) of the
framebuffer memory.

When I modify the framebuffer through a mmap I don't have any problems,
but when I switch to the console the kernel hangs.

I'm currently recompiling the kernel with FBCONDEBUG defined and I'll test
from there.

Any other suggestions on how to approach this?

Thanks,

---

Rick


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