Re: Linux 2.4.29-pre1 (was: Re: [PATCH] vga16fb: Fix frame buffer bad memory mapping)

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

On Sat, Nov 27, 2004 at 04:54:12PM +0100, Geert Uytterhoeven wrote:
> On Thu, 25 Nov 2004, Linux Kernel Mailing List wrote:
> > ChangeSet 1.1543, 2004/11/25 13:16:49-02:00, vince@arm.linux.org.uk
> > 
> > 	[PATCH] vga16fb: Fix frame buffer bad memory mapping
> > 	
> > 	The vga16fb driver uses a direct ioremap on 0xa00000 to gain access to
> > 	the vga card. This is wrong on architectures other than x86, every
> > 	other driver uses VGA_MAP_MEM macro from vga.h to ensure the correct
> > 	memory mapping.
> > 	
> > 	All this patch does is add the mapping macro this has been tested and
> > 	works on ARM systems The driver no longer maps parts of kernel
> > 	workspace and modifies it.
> 
> This fix is not correct!
> 
> > diff -Nru a/drivers/video/vga16fb.c b/drivers/video/vga16fb.c
> > --- a/drivers/video/vga16fb.c	2004-11-25 15:01:51 -08:00
> > +++ b/drivers/video/vga16fb.c	2004-11-25 15:01:51 -08:00
> > @@ -142,7 +142,7 @@
> >  	memset(fix, 0, sizeof(struct fb_fix_screeninfo));
> >  	strcpy(fix->id,"VGA16 VGA");
> >  
> > -	fix->smem_start = VGA_FB_PHYS;
> > +	fix->smem_start = VGA_MAP_MEM(VGA_FB_PHYS);
> >  	fix->smem_len = VGA_FB_PHYS_LEN;
> >  	fix->type = FB_TYPE_VGA_PLANES;
> >  	fix->visual = FB_VISUAL_PSEUDOCOLOR;
> 
> fix->smem_start: Although I agree VGA_FB_PHYS is not the correct value on
> machines other than PC, VGA_MAP_MEM(VGA_FB_PHYS) is not appropriate either,
> because fix->smem_start is supposed to be a CPU _physical_ address, not a
> virtual address.
> 
> However, this value isn't really used, except by (very rare) userspace that
> wants to mmap the frame buffer through /dev/mem instead of /dev/fb*, so an
> incorrect value doesn't really harm.
> 
> > @@ -896,7 +896,7 @@
> >  
> >  	/* XXX share VGA_FB_PHYS region with vgacon */
> >  
> > -        vga16fb.video_vbase = ioremap(VGA_FB_PHYS, VGA_FB_PHYS_LEN);
> > +        vga16fb.video_vbase = ioremap(VGA_MAP_MEM(VGA_FB_PHYS), VGA_FB_PHYS_LEN);
> >  	if (!vga16fb.video_vbase) {
> >  		printk(KERN_ERR "vga16fb: unable to map device\n");
> >  		return -ENOMEM;
> 
> ioremap(): VGA_MAP_MEM() already a _virtual_ address:
> 
> | include/asm-alpha/vga.h:#define VGA_MAP_MEM(x)   ((unsigned long) ioremap((x), 0))
> | include/asm-arm/vga.h:#define VGA_MAP_MEM(x)     (PCIMEM_BASE + (x))
> | include/asm-i386/vga.h:#define VGA_MAP_MEM(x) (unsigned long)phys_to_virt(x)
> | include/asm-ia64/vga.h:#define VGA_MAP_MEM(x)    ((unsigned long) ioremap((x), 0))
> | include/asm-mips/vga.h:#define VGA_MAP_MEM(x) ((unsigned long)0xb0000000 + (unsigned long)(x))
> | include/asm-ppc/vga.h:#define VGA_MAP_MEM(x) (x + vgacon_remap_base)
> | include/asm-ppc64/vga.h:#define VGA_MAP_MEM(x) ((unsigned long) ioremap((x), 0))
> | include/asm-sparc64/vga.h:#define VGA_MAP_MEM(x) (x)
> | include/asm-x86_64/vga.h:#define VGA_MAP_MEM(x) (unsigned long)phys_to_virt(x)
> 
> Doing a double ioremap(), or ioremap(phys_to_virt()) will break for sure...
> 
> BTW, on (PReP/CHRP) PPC ioremap() on ISA memory space `just works' because
> __ioremap() adds _ISA_MEM_BASE to the passed pointer if it's smaller than
> 16*1024*1024. And yes, vga16fb used to work fine on my CHRP LongTrail
> (before the machine itself died :-(.
> 
> Yes, ISA memory space is a mess to do right in a portable way...

Geert, 

I'll guest I'll just revert the whole change then... Do you have a
better suggestion? 

Thanks!