lkml.org 
[lkml]   [2006]   [Nov]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] fbcon: Re-fix little-endian bogosity in slow_imageblit()
On Fri, 03 Nov 2006 15:55:34 +0100
Franck Bui-Huu <vagabon.xyz@gmail.com> wrote:

> From: Franck Bui-Huu <fbuihuu@gmail.com>
>
> This bug has been introduced by commit:
>
> a536093a2f07007aa572e922752b7491b9ea8ff2
>
> This commit fixed the big-endian case but broke the little-endian one.
> This patch revert the previous change and swap the definition of
> FB_BIT_NR() macro between big and little endian. It should work for
> both endianess now.
>

I get worried when I see the word "should" in a changelog.

> ---
>
> This is the most obvious fix for me although it's a bit weird
> that bit ordering depend on platform endianess. I don't know
> fb code so I prefer submitting this trivial fix rather than
> breaking every thing else ;)
>
> drivers/video/cfbimgblt.c | 4 ++--
> include/linux/fb.h | 2 ++
> 2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/cfbimgblt.c b/drivers/video/cfbimgblt.c
> index 51d3538..8f47bf4 100644
> --- a/drivers/video/cfbimgblt.c
> +++ b/drivers/video/cfbimgblt.c
> @@ -168,7 +168,7 @@ static inline void slow_imageblit(const
>
> while (j--) {
> l--;
> - color = (*s & (1 << l)) ? fgcolor : bgcolor;
> + color = (*s & (1 << FB_BIT_NR(l))) ? fgcolor : bgcolor;
> val |= FB_SHIFT_HIGH(color, shift);

So that takes us back to the pre-March 31 code, which was allegedly broken
on big-endian.


> --- a/include/linux/fb.h
> +++ b/include/linux/fb.h
> @@ -854,10 +854,12 @@ #define fb_memset memset
> #endif
>
> #if defined (__BIG_ENDIAN)
> +#define FB_BIT_NR(b) (b)
> #define FB_LEFT_POS(bpp) (32 - bpp)
> #define FB_SHIFT_HIGH(val, bits) ((val) >> (bits))
> #define FB_SHIFT_LOW(val, bits) ((val) << (bits))
> #else
> +#define FB_BIT_NR(b) (7 - (b))
> #define FB_LEFT_POS(bpp) (0)
> #define FB_SHIFT_HIGH(val, bits) ((val) << (bits))
> #define FB_SHIFT_LOW(val, bits) ((val) >> (bits))

And that swaps the little-endian and bit-endian implementations of
FB_BIT_NR(). So if it was previously broken on big-endian and was working
on little-endian then it's presumably now broken on little-endian and
working on big-endian. Or something.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-11-03 20:01    [W:0.084 / U:0.588 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site