Re: CONFIG_VGACON_SOFT_SCROLLBACK crashes 2.6.17

["Antonio Vargas" <windenntw@gmail.com>]

On 6/22/06, Antonino A. Daplas <adaplas@gmail.com> wrote:
> Al Boldi wrote:
> > Antonino A. Daplas wrote:
> >> Al Boldi wrote:
> >>> Enabling CONFIG_VGACON_SOFT_SCROLLBACK causes random fatal system
> >>> freezes.
> >>>
> >>> Especially, ping 10.1 -A easily causes a complete system hang during
> >>> scroll.
> >>>
> >>> Is there an easy way to fix this, other than disabling the option?
> >> I can't duplicate your problem. Did it ever work before?
> >
> > This option did not exist before 2.6.17.
>
> I meant if you tried any of the -rc kernels.
>
> Anyway, can you try the patch below.  It's a debugging patch and
> it will slow down the console.
>
> If the system hang disappears, remove the line
>
>     while (i--);
>
> in include/linux/vt_buffer.h.  This line is introduced by
> the patch below.
>
> Let me know at what point it worked, or whether it worked at all.
>
> >
> >> Can you send me you kernel config?
> >
> > Attached below.
> >
> > BTW, is there any chance to patch your savagefb to support VIA/S3 UniChrome?
> >
>
> If someone posts a patch to lkml or fbdev-devel, why not?  But a separate
> driver is probably better as the 2 are very different.
>
> Tony
>
> diff --git a/include/linux/vt_buffer.h b/include/linux/vt_buffer.h
> index 057db7d..e9b6064 100644
> --- a/include/linux/vt_buffer.h
> +++ b/include/linux/vt_buffer.h
> @@ -20,11 +20,21 @@ #endif
>
>  #ifndef VT_BUF_HAVE_RW
>  #define scr_writew(val, addr) (*(addr) = (val))
> -#define scr_readw(addr) (*(addr))
> -#define scr_memcpyw(d, s, c) memcpy(d, s, c)
> -#define scr_memmovew(d, s, c) memmove(d, s, c)
> -#define VT_BUF_HAVE_MEMCPYW
> -#define VT_BUF_HAVE_MEMMOVEW
> +//#define scr_readw(addr) (*(addr))
> +
> +static inline u16 scr_readw(volatile const u16 *addr)
> +{
> +    int i = 10000;
> +    u16 val = *addr;
> +
> +    while (i--);
> +    return val;
> +}
> +
> +//#define scr_memcpyw(d, s, c) memcpy(d, s, c)
> +//#define scr_memmovew(d, s, c) memmove(d, s, c)
> +#undef VT_BUF_HAVE_MEMCPYW
> +#undef VT_BUF_HAVE_MEMMOVEW
>  #endif
>
>  #ifndef VT_BUF_HAVE_MEMSETW

Antonino, is this while(i--) a cpu busy-wait loop??? This would have
different timings on different cpu kinds... maybe a short usleep()?