Re: [PATCH] offb: Fix little-endian support

[Takashi Iwai <tiwai@suse.de>]

At Wed, 14 May 2014 16:01:17 +0200,
Cedric Le Goater wrote:
> 
> Hi Iwai-san,
> 
> On 05/14/2014 03:21 PM, Takashi Iwai wrote:
> > Although the color palette was corrected for little endian by the
> > commit  [e1edf18b: offb: Add palette hack for little endian], the
> > graphics mode is still shown in psychedelic colors.  
> 
> Are you referring to the linux logo colors ? If so, could you please
> try the patch below, it should be a fix.

Not only penguin logo but the whole X graphics got strange colors,
too, according to the bug report.  I put the original reporter/tester
(Dinar Valeev) to Cc.
I'm merely a person who tries to fix this mess ;)

BTW, did you try to run X on fbdev?

> > For fixing this
> > properly, we rather need to correct the RGB offsets depending on
> > endianess.
> > 
> > Since the RGB base offsets are corrected, we don't need the hack for
> > pallette color entries.  This patch reverts that, too.
> 
> Are you testing using qemu -vga std -vnc :x ? If so, did you try changing 
> the depth to 8,15,16,32 ?

Yes, it was with qemu -vga std -vnc :x.
About different color depths, Dinar can test / clarify better, I
suppose.

>  I think the patch might be breaking big endian 
> too.

Big endian should work as is because my patch uses the original
offsets when fb_be_math() is true.  It corrects the RGB offsets if
!fb_be_math().

But, I'm also entirely not sure whether this is 100% correct, either.
Namely, if the RGB offsets were correct for some little endian
machines with offb, my patch would break it, of course.  But, then
your previous fix must have already broken it as well, so I took the
same fb_be_math() check.


thanks,

Takashi

> Now, I am far from being an expert on frame buffers. It would be glad 
> to have some insights on that topic. 
> 
> Thanks,
> 
> C. 
> 
> 
> [PATCH] fb: fix logo palette entries for little endian
> 
> The offb_cmap_byteswap() routine helps byteswapping the color map
> entries when required. This patch externalizes and renames the helper 
> routine to adjust the pseudo palette of the logo when running on 
> little endian.
> 
> Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
> ---
>  drivers/video/fbmem.c |    6 ++++--
>  drivers/video/offb.c  |   11 +----------
>  include/linux/fb.h    |    8 ++++++++
>  3 files changed, 13 insertions(+), 12 deletions(-)
> 
> Index: linux.git/drivers/video/fbmem.c
> =================================> --- linux.git.orig/drivers/video/fbmem.c
> +++ linux.git/drivers/video/fbmem.c
> @@ -252,7 +252,8 @@ static void  fb_set_logo_truepalette(str
>  	blueshift  = info->var.blue.offset  - (8 - info->var.blue.length);
>  
>  	for ( i = 0; i < logo->clutsize; i++) {
> -		palette[i+32] = (safe_shift((clut[0] & redmask), redshift) |
> +		palette[i+32] = fb_cmap_byteswap(info,
> +				 safe_shift((clut[0] & redmask), redshift) |
>  				 safe_shift((clut[1] & greenmask), greenshift) |
>  				 safe_shift((clut[2] & bluemask), blueshift));
>  		clut += 3;
> @@ -271,7 +272,8 @@ static void fb_set_logo_directpalette(st
>  	blueshift = info->var.blue.offset;
>  
>  	for (i = 32; i < 32 + logo->clutsize; i++)
> -		palette[i] = i << redshift | i << greenshift | i << blueshift;
> +		palette[i] = fb_cmap_byteswap(info, i << redshift |
> +					i << greenshift | i << blueshift);
>  }
>  
>  static void fb_set_logo(struct fb_info *info,
> Index: linux.git/drivers/video/offb.c
> =================================> --- linux.git.orig/drivers/video/offb.c
> +++ linux.git/drivers/video/offb.c
> @@ -91,15 +91,6 @@ extern boot_infos_t *boot_infos;
>  #define AVIVO_DC_LUTB_WHITE_OFFSET_GREEN        0x6cd4
>  #define AVIVO_DC_LUTB_WHITE_OFFSET_RED          0x6cd8
>  
> -#define FB_RIGHT_POS(p, bpp)         (fb_be_math(p) ? 0 : (32 - (bpp)))
> -
> -static inline u32 offb_cmap_byteswap(struct fb_info *info, u32 value)
> -{
> -	u32 bpp = info->var.bits_per_pixel;
> -
> -	return cpu_to_be32(value) >> FB_RIGHT_POS(info, bpp);
> -}
> -
>      /*
>       *  Set a single color register. The values supplied are already
>       *  rounded down to the hardware's capabilities (according to the
> @@ -129,7 +120,7 @@ static int offb_setcolreg(u_int regno, u
>  			mask <<= info->var.transp.offset;
>  			value |= mask;
>  		}
> -		pal[regno] = offb_cmap_byteswap(info, value);
> +		pal[regno] = fb_cmap_byteswap(info, value);
>  		return 0;
>  	}
>  
> Index: linux.git/include/linux/fb.h
> =================================> --- linux.git.orig/include/linux/fb.h
> +++ linux.git/include/linux/fb.h
> @@ -582,6 +582,7 @@ static inline struct apertures_struct *a
>  
>  #endif
>  
> +#define FB_RIGHT_POS(p, bpp)         (fb_be_math(p) ? 0 : (32 - (bpp)))
>  #define FB_LEFT_POS(p, bpp)          (fb_be_math(p) ? (32 - (bpp)) : 0)
>  #define FB_SHIFT_HIGH(p, val, bits)  (fb_be_math(p) ? (val) >> (bits) : \
>  						      (val) << (bits))
> @@ -681,6 +682,13 @@ static inline bool fb_be_math(struct fb_
>  #endif /* CONFIG_FB_FOREIGN_ENDIAN */
>  }
>  
> +static inline u32 fb_cmap_byteswap(struct fb_info *info, u32 value)
> +{
> +	u32 bpp = info->var.bits_per_pixel;
> +
> +	return cpu_to_be32(value) >> FB_RIGHT_POS(info, bpp);
> +}
> +
>  /* drivers/video/fbsysfs.c */
>  extern struct fb_info *framebuffer_alloc(size_t size, struct device *dev);
>  extern void framebuffer_release(struct fb_info *info);
>