On Tue, 22 Apr 2008, Scott D. Davilla wrote:

quoted

 > On Tue, 22 Apr 2008, Scott D. Davilla wrote:
 > >  >On Tue, 22 Apr 2008, Benjamin Herrenschmidt wrote:
 > >  >>  We currently have a problem with those two members of struct
 > >  >>  fb_fix_screeninfo. The struct contains an "unsigned long" 
which means
 > >  >>  that:
 > >  >>
 > >  >>  - 64 bits kernels with 32 bits userspace can't pass a complete

 > > > address

quoted

 > >  >>  - 32 bits machines with 64 bits resource_size_t can't 
pass a complete
 > >  >>  address
 > >  >>  - The structure isn't even properly padded to be 32/64 bits neutral
 > > in
 > >  >>  the first place.
 > >  >>
 > >  >  > We could define new versions of the struct with new 
get/set ioctls,
 > >  >>  or we could try to just deprecate those fields. What do you guys
 > > think ?
 > >  >
 > >  >As userspace doesn't really need those fields[1], we can easily
 > >  >deprecate them.
 > >
 >  > kexec uses FBIOGET_FSCREENINFO and FBIOGET_VSCREENINFO. So if these
 >  > ioctls changes, it will possibly break kexec under vesafb and efifb.
 >
 > Does kexec use the smem_start and mmio_start fields of
 > fb_fix_screeninfo?
 >

 In "kexec/arch/i386/x86-linux-setup.c", the routine 
"setup_linux_vesafb" uses
 smem_start, smem_len, and line_length.

 This is used for vesafb and efifb framebuffer kernel boot param 
setup. This is
 required for PC hardware that do not contain a PC-BIOS and need 
the bootloader
 to setup the kernel video boot params.

OK, but the problem doesn't show up on x86-32 (no >32-bit physical
addresses yet), as x86_linux_param_header.lfb_base is uint32_t and there's no
way it's gonna change.

I seem to remember the EFI/kexec guys have been doing kexec from 
32->64 kernel and I think 64->32. I'm 32 bit only so I have no 
experience under 64 bit kernels and don't really pay much attention 
to 64 bit kernel patches. Huang Ying was doing the EFI/kexec patches 
a few months ago.



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