[okl4-developer] Starting with graphic output

[Remy Gottschalk]

On Fri, 2008-04-25 at 21:55 +1000, Geoffrey Lee wrote:
> 
> Hi Remy
> 

Hi 
> 
> > 
> > > As a quick fix you may be able to add a quick hack to eas_map() to 
> > > add backdoor range check for your framebuffer physical range.
> > 
> > Strangely it seems that my mmap request doesn't arrive to eas_map. I
> > don't really understand what this could means.
> > 
> 
> How are you mmaping the device?  mmaping memory in userspace should arrive at 
> eas_map(), this suggests to me that it is failing some check earlier on.  
> I suggest using printk() or similar to trace the execution to find 
> out where and why exaclty the mmap() call is failing.
> 
> 	-gl
> 

I did what you suggested and tracked down where the mmap call fail and
what I found is pretty unexpected.
So if I open the framebuffer with RW rights.
fb_fd = open("/dev/fb0", O_RDWR);
When i mmap it 
fb_p = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,
                   fb_fd, 0);

My mmap call goes its way to do_mmap_pgoff in mm/mmap.c and fail at a
basic check :
if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE))
	return -EACCES;
This check only verify if when asking a mapping with write access the
file is open with write right.

And when I open the device with writing right only (witch is sufficient
after all since i just want to get my framebuffer uggly :) ) it all goes
fine and I get the good old roottask pagefault at 0x18.

By the way the open goes fine and return no error. Furthermore I can
achieve successful ioctls on the device such as blank screen and
retrieving information structures.

I didn't dig in more for now but it seems that there some problem with
file rights.

I guess I will wait a little before playing with framebuffer or use it a
different way.

Regards,


-- 
Remy Gottschalk - rgottschalk at linagora.com
Ingénieur informatique embarquée
Groupe LINAGORA - http://www.linagora.com
Tél.: +33(0)1 58 18 68 28 - Fax : +33(0)1 58 18 68 29